Visit your Card page, then click on a Mutual Friend's icon to view their cards. Once you see a card you would like to trade for, click 'initiate trade' to the right of your friend's icons.

From there, click on the card(s) your friend has on the top row that you would like, then click a card(s) from your hand on the bottom row that you would be willing to trade for.

Then, click 'offer trade'. Your friend will then accept or reject the trade.

Cancel Trade
If you changed your mind about a trade offer, follow these steps:
1. Go to your cards.
2. Find the card(s) selected for the Trade. There will be a red ribbon in the top-right corner with the user's icon. 
3. Click on the user's icon to reveal the "cancel trade" option.
4. Click "cancel trade". The trade has now been canceled.