Trade Window

Buttons
Item Tabs
These consist of Furnishing, Pins, CLothing, and Posters. Clicking on these tabs will change the items in the item box (The item box is the large box between the item tabs and trade windows that can display up to 14 items at a time.
Accept Buttons
To accept a trade, click the little blue box next to "You accept". A small X should appear in it. Sometimes you will be asked if you're sure you want to make the trade. Once both players have accepted, you will be asked one final time if you want to accept the trade.
Ask to be friend / Stop trading
These buttons are self explanatory. The first asks the other trader to be your friend, and the other closes the trade window.