When you create a membership, you have the option to add credits to it. Credits can be used to either put a restriction on the membership, or to add a little extra.
What you need to do before adding credits to your memberships, is make sure you have all the services you offer added under "services" in business settings. Some service examples: personal training, bootcamp, tanning salon or group session.
If you would now create a membership, you see all the services you've put in under the section "credits".
Example for using credits: If you sell your member a membership that allows them 1 personal training session per week, and 2 group sessions a month, you can use credits for this.
If you would now assign this membership to your member, you will see he will receive 1 personal training credit each week and 2 group session credits per month. You can manually deduct or add credits for your administration. If you have attached credits to scheduled activities and you book a client for one of those activities, the credits will be deducted automatically.