You will get a call from Lester -- and his L symbol will appear on your map -- once you reach a certain point in the game, at which point you can go pay him a visit and have a chat with him during which he will suggest to you that it is a very good idea for you to purchase property -- this is the game's way of reminding you that you can buy a safe house or a garage (not both).
In addition to sharing that bit of advice with you, Lester also shares the details of the Bounty System that you now have access to, through him.
Basically you can ring Lester and place a Bounty (for a price) on another player. And they can do the same to you!
There is actually an Achievement in the game for this -- it is called "Run Like the Wind" (20G) GTA online: Survive for a day with a Bounty on your head. As it says, the way to unlock that Achievement is to last one in-game day (about 45 minutes) with a Bounty on you.
Needless to say that can be tricky if there are other players on the server you happen to be playing on because they will be made aware that you have a Bounty and will likely try to collect it!
You are welcome. The tutorial for this part actually is part of the first mission and its CSs you will play with Lester so just go to his icon and follow the instructions he gives.
Thank you but don't know how to get to the tutoral