Actually, Clarr switched the buy items bit to the Actions page. So:
[Position] -> [Actions] -> then choose the buy items/shopkeeper option that is there. Once you buy an item, it will drop at your feet. You will then need to click on the [Equipment] link on the sidebar (under where you clicked [Position]) and then drag the item(s) you bought onto the slots on the image of a man on the left of that page.
Just beware that likely there will be other items that other players have bought but not picked up, so check (using the inventory page on the sidebar to the right - if you picked it up it should say in location: Equipped by Kit Kuran
) that the item is yours. May save frustration later.