Mostly, they don't have controls. There are mainly applied where necessary by the system. Walking towards a hidden item or trap applies perception automatically. If you click on a trap, your character with the highest trickery walks up and attempts to take care of it. If you pick up a magic item, your best lore test will be performed so that when you look in inventory the item is identified. Etc.

There is a specific, tiny button to turn stealth on and off, on the right-hand side of the ui.

I think most of this stuff becomes obvious during the tutorial portion of the game, so do read through the pop-ups.