First, go into your game, click the left option.

Choose  “My Team”

Click “ VIEW ITEMS”

There are cards you own, click any of them, then it appeared the next pic.

Remember: if the option ”POST” is gray, means you cant sell him, then you should choose another player.

Click  “POST” ，set the start bid, buy now price and duration. 

Last steps click “POST AUCTION” .

If you want check the player you posted, just choose the left option then click the “AUCTIONS”.

 

ADVICE: its more easier to find and buy your card if you set the start bid with 84516.