CiviEvent - capturing billing information, interaction (or not) with contacts
When you say registration, do you mean "of membership"?

If it's just registration of being part of your organisation, perhaps attach it to an activity of type "Registration" on the contact.

However, your message concerned me. In general CiviCRM isn't used for credit card information - there are a lot of laws surrounding how that information is stored. Tangentially, you should also read: https://en.wikipedia.org/wiki/Payment_Card_Industry_Data_Security_Standard

In general we would advocate using a dedicated payment processor extension and only storing transaction Ids in Civi.