Some subscriptions work with credit: a number of classes per month, or a punch card you use whenever it suits you.
Types of credit. Class credit for the timetable, and sometimes separate credit for, say, personal training. What’s meant for one type can’t be used for the other.
Your balance. Classes shows how many visits you have left, or that yours is unlimited. Under Profile → Your subscription you see what your subscription gives you per period and how long it’s valid.
When a visit is deducted. When you book, not when you attend. That way your place is secured.
Cancelling. If you cancel in time, you get the visit back. What counts as in time is set by your gym; it’s shown with the class. If you cancel too late or don’t turn up, the visit may be used up.
Validity. Credit often has an expiry date. Expired visits don’t come back.
Buying more. You buy a punch card under Your subscription, or in your gym’s shop. If you were given a visit as a gift or a class didn’t go ahead, your gym can add visits.