I opened up the college but can't select an item to be appraised.. can you tell me how?

In the college screen you should see the Professor Ayanna Farmer and a button on the right that says Select an Item. Tapping this will show you your inventory with any Rare items that need to be appraised. If you don't see anything then perhaps you don't have any items to be checked.

When doing the auction an item you click on to see how much it's worth says " that looks interesting" or something of that nature will need to be appraised to find out if it's real or fake. In your inventory the items you can take to the college will have a magnifying glass in the top left of the item