You're a drug dealer. Your job is to provide other players with drugs.
Players will call for you with the drugdealer command. Once they finally call for you, you can sell them the amount of drugs they want using the giveweed command and the giveheroin command. (example: /giveweed (player name/id) 10 will give a player 10 grams of weed, the same with heroin)
Beware tho, every time you sell a player drugs your wanted level increases and a police officer can search you for drugs and arrest you if he finds that you carry them. So don't go asking players in the main chat if they want drugs, use the private message command or the whisper command.
If you run out of drugs to sell you can always restock in the drug houses you can find around San Fierro as they are marked with a "D" on the map.