One of the Goals you can receive is to Complete X Trades. Trades are a good way to get rid of excess Cards and earn more Buds.
Trades are offered by Shorty at the bottom of your screen:
She asks for Cards you have in exchange for Buds:
It's up to you to decide if it's a worthwhile deal! If you don't think it's valuable, don't worry, Shorty will offer a Trade (should you have the criteria met for any of her trades in a given episode/event) approximately every hour. Be sure to check out the deal even if you're just stopping in to open your Zeke Chest!
You can also get Trades in Events for Event Buds or Cards!