How does one use skills in this game? It seems simple but the menu for the controls is strange.

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.

Thank you. I am very used to the old D&D games where most skills were manual.