welcome to the forums leayha001
to get the steal expression you must upgrade your guile to level 3.
NOTE:you can only use it on items you find lying around/items on display in a shop.
you must leave the button down until the item is yours.
you can also steal items from all the cabinets you find.
just look at it and press Tab(pc)/A(xbox)
NOTE:you dont need guile/steal expression to steal from cabinets.
stealing is instant.