"To begin the mission, go to the Bam Bam club. You have to take a Winston and drive him on a meeting with the Uncle Po.
Man will ask you to get a debt from the woman. As soon as you approach to her, she'll start running.
Chase her quickly, shooting out her guards on the way. The best way is to fire at their tires. To fire, hold L1 and press R2.
When the woman stays alone, approach her car and jump inside (hold and press X). A moment later she'll tell you that she has a lot of drugs in the trunk.
Drive them to the garage suggested by Roland what ends the mission. Now you have an access to the new flat and missions basing on getting debts paid. To begin such type of a mission, you need to call Roland and go to the marked point on the map.