Escuela of the Streets
He first instructs you to get a vehicle and follow a group of drug dealers as they move through the streets of Bohan in a car. You must be careful not to get too close to their car, or they will spot you. Follow the drug dealers' car until they arrive at a run-down warehouse, and then park behind them. After a short cutscene, Manny tells you to follow the dealers into the warehouse and then kill them.
You will quickly find that the door used by the dealers to enter the warehouse is locked. You must find another entrance, and if you take long enough, Manny will send you a text message saying that for every door that closes, a window opens. This is a hint to enter the warehouse through one of its windows. There are two large windows at the front of the warehouse, to the left of the locked door. Shoot one of them with a firearm to break the glass, and then climb on to the ledge and into the warehouse. The shooting of the glass will startle the drug dealers inside the warehouse, so they will be ready for you as you enter, and it may even alert the police.
Once inside the warehouse, take cover behind one of the many stacks of boxes, and shoot all of the drug dealers (there are roughly five or six of them). When all of them have been killed, you can leave the warehouse and Manny will pick you up. However, if the cops have been alerted, you will need to lose your wanted level first.