Thieving allows players you steal & pickpocket gold from npcs (items & market stalls later). Stuns do 10% of your max HP, so be careful.
Right-click > activate thief's tools located in your inventory and click on the following npcs...
Level 1: Man/Woman -- 10xp -- 10gp
Level 10: Farmer -- 30xp -- seeds
Level 25: Al-Kharid warrior -- 50xp -- 20gp
Level 32: Rogue -- 100 xp -- 30gp
Level 38: Master farmer -- 75xp -- all seeds
Level 40: Guard -- 100xp -- 40gp
Level 45: Beard Pol Guard -- 150xp -- 50gp
Level 53: Desert Bandit -- 200xp -- 100gp