You can fill in your card details and billing address in the Billing details section, which you can find under Settings (the gear icon in the bottom left corner).
You'll need to have this section filled in when you have an active subscription. The payment is automatic, so a credit card is required for the subscription to continue.
You can update and delete your billing details directly in your account as you need to. The changes are saved automatically, so there's no need to do anything else.
Each team has its own subscription and billing details. So if you're a Team Owner or Team Admin for more teams, then you'll see the Billing details for each one of them.