Multiplayer in GTA IV

Multiplayer in GTA IV is a new, fully fleshed-out feature for Grand Theft Auto IV. The multiplayer features:

A total of 15 game modes divided into three main categories (Player Match, Ranked and Party Mode), each with unique objectives and gameplay types.
A maximum number of players is 16, although various modes have limitations on the number of players that can join.
Configuration of each mode can be adjusted by the host. Vehicles types, volume of traffic, number of pedestrians, police presence, weapons, auto-aim and weather can all be controlled.
Characters are completely customizable. You can essentially create your own unique online character by adjusting their hair, sex, race, clothing etc. *Additional options can be unlocked by increasing your rank in Ranked multiplayer matches. However, players won't be able to customize shoes, facial hairs, even hairstyles.
Games are, in essence, random. Upon choosing a game mode to play, you will either be thrown into an already made game or you will start your own.
Killing another player will get you $100. A dead player will usually drop approximately $15. Killing yourself will cause you to lose $100. Killing police officers will not reward you money (except in Hangman's NOOSE), but will only drop weapons as a reward to supply more ammunition.
Ranked matches, like everything else in multiplayer GTA, requires money to get ahead. The amount needed to gain a rank increases exponentially as you progress.

Starting Multiplayer

ACCESSING MULTIPLAYER

To jump into multiplayer, do the following:

Bring up your mobile phone.
Access the cellphone menu.
Scroll down to Multiplayer.
Enter the Multiplayer submenu, at which point you can access multiplayer matches, customize your character or view a multiplayer tutorial.

The multiplayer tutorial will give you all of the information you need to know to jump into multiplayer games, and is a great way to introduce yourself to the dynamics of multiplayer Grand Theft Auto.

You do not actually need to have completed It's Your Call and gotten the cell phone. If you attempt to use the cell phone before Roman gives it to Niko, you will only see the multiplayer option on the menu.

Game Types

Player Match

Player Match lets you go up against other GTA gamers in every possible multiplayer mode. This is about fun more so than bragging rights; who scores what for each game is irrelevant once the time is up. This is a great way to relax, have fun, chat with other people and enjoy Grand Theft Auto for the sake of enjoying Grand Theft Auto. It's also a good way to get a feel for the different modes before jumping into Ranked matches.

Ranked Match

Ranked Matches -- either on PSN or Xbox Live -- are for those of us who need true motivation, and a massive e-peen to boot. Every Ranked match you enter puts you up against opponents who are playing to win. The word "fun" doesn't mean a damn thing here. As you progress in Ranked matches and earn more money, your rank will gradually increase (maximum ranked level is 10), unlocking additional goodies (clothing, basically) for your multiplayer character.

Party Mode

A VIP, invite-only variant of Free Mode. Party Mode throws everyone on the same team and sets everyone to respawn in the exact same location (complete with every single weapon imaginable, as well as vehicles, First Aid kits and body armor). There are also no police in Party Mode. As the name would suggest, Party Mode is great for running around in Liberty City and causing all hell to break loose.

Free Mode

Like single-player, except playing with your friends. Complete free for all. No rules, no objectives, no score. You're free to do whatever you wish. Keep in mind that Free Mode is only doable through non-ranked Player Matches. The police will be present and shoot the player on sight (if the host turns on the Police, for more twist). It still reads "PSN/XBL name Died", despite that Police/FIB/NOOSE killed the players. The police will not arrest players, but will shoot them instead.

Modes

Team Modes

Mode	Players	Objective
Team Deathmatch	2-16 (up to 8 teams of two)	Players work as a team to rub out other team(s) for money - and the crew with the most cash at the end of the round wins. There's no restrictions - do whatever it takes to rub out the competition. You get the ash you've earned by killing the other teams members. If you kill no one you get no reward. Police will be present in the game (NOOSE/FIB at 4 wanted level stars), and they do whatever they can to kill other players from shooting at each other (if the host turns on the Police).
Team Mafiya Work	2-16 (up to 8 teams of two)	You're a member of a crew doing contract work for the mafiya - including such plum gigs as escorting wanted men, picking up MacGuffins and stealing cars. Work as a team to complete contracts before the time period ends and get the rewards. You'll probably want to do your best to scupper the other crew's work as well. Each contract you complete gives your team cash, and the crew with the most cash at the end of the round wins.
Team Car Jack City	2-8 teams	Cars spawn in random places on the map and the teams must steal them and take them to a drop off point. The cash teams get for dropping off stolen vehicles depends on their condition - teams get less cash the more damaged they are. There are exceptions though: some are special bonus cars, containing drugs, which give a set amount of cash on delivery no matter how damaged they are. If the vehicles sustains heavy damage, then players receives less money. Your crew has to get hold of whatever vehicles the boss wants. Police will be present as well, and will do whatever they can to stop players from taking vehicles (what Petrovic requires, and if the host activates Police) into drop-off points. Whichever crew makes the most money wins.
Cops N' Crooks	4-16 (two teams only)	A team-based mode in which the Crooks must get their Boss to safety (they won't be able to know where the cops are, because purple dots aren't denoted), while the Cops have to take him down. The Boss is marked with a cross hair. This mode has two sub-modes: All for One and One for All. In All for One, one team is made up of Crooks and a Boss, and the other team is made up of Cops. The Cops are trying to hunt down and kill the Boss while the Crooks are trying to protect him. The Cops win by killing the Boss and the Crooks win by getting the Boss safely to the getaway vehicle and escaping. One for All is similar but there is no Boss. Here, the Cops win by killing all of the Crooks, or destroying the getaway vehicle and the Crooks win by filling up a getaway vehicle with members of their team, or killing all the cops. Only 4 people can escape in the getaway vehicle. Players cannot respawn in this mode.
Turf War	2 teams only	A timed capture-the-base mode. There are a number of bases around the map that you have to take by standing near them for a short period of time. The more players that are on a base, the faster it can be captured. The more bases that your team owns, the faster your team's cash score increases. If the rival gang is on or near a base, you won't be able to take control of it. The team with the most cash at the end of the round wins.

Cooperative Missions

Mode	Players	Objective
Deal Breaker	2-4	Time to crash the party. You and your team will work together to bust in on a deal that's going down, take out anyone in attendance, grab the goods and wipe out the witnesses. Don't get busted, don't get killed, and walk away with a nice chunk of change.
Hangman's NOOSE	2-4	Single player mission that features co-op play. Mafiya boss Petrovic has illegally flown into Francis International Airport, and someone has tipped off the cops. The objective Escort Petrovic to safety while being pursued by the Liberty City Police Department's NOOSE (SWAT) division. You only have three respawns, so keep yourself from dying too often.
Bomb Da Base II	2-4	Bomb Da Base II tips its hat to Bomb da Base (from GTA3), one of the most outstanding Grand Theft Auto missions ever created. In Bomb da Base II, you and your cohorts will work in unison to sabotage a large cargo ship. Ample amounts of vehicle theft, police chases and gunfights are involved. Like HANGMAN's NOOSE, you can respawn up to three times before being dropped out of the mission.

Competitive Modes

Mode	Players	Objective
Deathmatch	2-16	It's a complete free for all! Anything goes, and you can use any tactics you like to kill off the competition. Combat is confined to specific areas of Liberty City in order to keep the action intense. Police (including NOOSE and/or FIB) will be present as well, depends whether the host has turned it on, and will also be involved into a Deathmatch and try their best to kill players shooting at each other, rather than arresting them.
Mafiya Work	2-8	Working under the direction of Kenny Petrovic via your cellphone, you will compete against other players in a series of mini-missions. You might have to pick up recruits for the firm or take out a target, or even find and then dispose of a dozen severed heads.
Car Jack City	4-16	What Petrovic wants, Petrovic gets. Car Jack City pits you against everyone else in a race to nab vehicles for the all-powerful Russian Mafiya boss. The ends justify the means, so do whatever it takes to grab all the cars. Just like Team Car Jack City, the amount of money you have trumps the amount of cars you've delivered. If the Police is activated by the host, Police will try and stop players from taking vehicles into drop-off points, so evade tham at all costs.

Race Modes

Mode	Players	Objective
Race	1-16	Race to the finish through each checkpoint in order: If you take a wrong turn or mess up in some way, you can respawn your vehicle on the last checkpoint you passed. There is a large selection of races for cars, boats, and helicopters - you can choose laps and vehicle class/type. Race has two types of races: Free Race and Cannonball Run. Free Races are point-to-point races, where the first one to the finish wins. Cannonball Runs are races where you have to traverse several checkpoints in any way you can.
GTA Race	1-16	Similar to the orthodox Race, but with the added element of combat. Race and fight your way through the checkpoints in order and then hit the finish, but this time you can also pick up the weapons spawned en route to help take out your opponents. You can also exit the vehicle during the road races.

Source

GTA IV Net - Multiplayer: Gametypes, Modes, Online