Converting allows you to change one spot asset into another.
You can convert on the wallet page. To do so, choose the asset you want to sell, and click 'CONVERT'; this will print up a panel. Enter the asset you'd like to buy with it. You'll then be quoted a price; if you want to execute that trade, you can.
There are no fees on conversions. Note that the price quoted will depend on market conditions. You can covert FTT, USD, USDT, BTC, ETH, BCH, LTC, and Leveraged tokens.