This may seem like a stupid question but how do you get the items you win at auction?  Because I got a notification email saying that I won a particular item but that item is not in my inventory nor can I find any record of the (now ended) auction in the trading tab.  I'm stumped!

If the item has an "autobuy" option, you pay the price of the auto-buy and the item is yours immediately.

If you're the highest bidder on an item when the auction time ends, you obtain the item.

It might take a few minutes to the item to appear in your inventory. If you know the item is an apparel item or something more unique, I'd check the inventory tabs based on if it's an invite, materials, alchemy-made items, tools, or things like the sundial and the microscope.