To start - make sure you have connected your wallet via the button that says "Connect a wallet" at the top of the page.
No tokens: If you don't see your tokens you own - there might be a problem loading their data, if we cannot fetch the data for the NFT, we won't display it (it would be broken).
Once you have your tokens loaded - you can choose to transfer them to another address or sell them on the marketplace.
Transfering: See how to transfer my tokens.
Selling: See how to sell my item