Thieving is a skill which allows players to obtain coins and items by stealing from market stalls, And also allowing players to unlock gear after you have received theft points from the chest north west of the stalls. To start this skill use the skilling teleport. Go to skilling area and talk to Harold then go to rogues den.

Image Stall Level reg legend
Bakery stall 1 2.100 300
Clothes stall 25 6.300 900
Crafting stall 50 12.600 1.800
Silver stall 75 21.000 3.000
Gem stall 90 37.700 5.100
Crafting stall 96 42.000 6.000

its a pretty straight forward skill