Virtual Card
Your virtual card is activated by default once you create it. You don't need to take any more steps to start using it, just make sure you have enough balance in your account.
You can use it to spend online, or add it to Google or Apple Pay to spend in-person.
Physical Card
Once you receive your physical card you can activate it directly in the Cards section within the app.
Go to the "cards" tab in your app
Select the physical card
Click on "Activate"
Once you do it you can start using your card wherever you go!
Make sure you only activate the card after you received it so no one else can use it.