Some gyms let you bring someone to a group class: a guest.
How. First book the class yourself. Then open the class in Classes and tap Bring a guest. Enter the first name and confirm your guest is fine with you passing it on. That's all.
Don't see the button? Then your gym doesn't allow guests, or you haven't booked that class yet.
How often. Your gym chooses how often per month you may bring someone. A guest you cancel does not count.
Cost. A guest costs no credit. You only pay for your own spot.
A full class. If there is room, your guest is booked straight away. Otherwise your guest goes on the waitlist, behind you. When a spot opens up, you get a notification.
Cancelling. If you cancel, your guest goes too. To cancel just your guest, tap Cancel guest on the class.
Privacy. Your gym only sees the first name, at the class. If your guest wants to know more or become a member, they arrange that themselves at the class; you don't pass on an email address or phone number. The first name is also in the data you can download, and is removed after 12 months.