One credit card account can sometimes have two (or more) credit cards issued on it. Every month the person who opened the account (called the main cardholder) is sent a bill. The bill lists all of the things bought by both the main cardholder and the additional cardholder(s). The main cardholder is responsible for paying the bill, whoever made the purchases. There is a limit for the account on the total amount that can be spent with the card each month. The limit applies to both the main and the additional cardholders. It is called a credit limit.
When you have a credit card you can add an additional card to the account for use by someone else. For example, your parents could add a credit card to their own account for you to use, but this will not help you build credit. The main cardholder has responsibility for ensuring payments on the additional card are made. All purchases are shown on the monthly credit card statement.
When you have a credit card, it is often possible to add an additional card to the account for use by someone else. The main cardholder holds responsibility for ensuring payments on the additional card are made. Purchases are shown on the credit card statement, which is sent monthly.