You are a hitman, your job is to kill players on your hit list and maniacs (Players on the map marked with the color).
You can check who is on your hitlist using the /hitlist command.
Players will often place a hit on others for killing, arresting, raping or kidnapping them for a amount of money (from $20,000 and up). When you kill the players on the hit list you will gain a wanted level and the police will go after you unless you bribe.
If you kill maniacs you will not gain a wanted level, you will gain a reward of $15,000.
But beware, the players you attack (no matter if they are a maniac or a player on the hit list) will be able to kill you too so you better be equipped for a fight.