From their home screen your customer can see how many credits they have left on the right hand side of the screen within the orange box.
Your customer can add more credits to their account in one of two ways:
Subscribe to a higher tier plan
Purchase them a-la-carte style
They can do either of those by selecting "buy more". On the following screen they can see upsells to upgrade their membership plan, purchase a bundle of credits, or purchase a specific number of credits.
What they see after clicking "buy more":
Your customer can use those credits towards coaching sessions at anytime. They can see how many credits each coach session costs by clicking on "video analysis" or "Live call" (if you offer those) and the cost per session is listed below:
Your customers credits will rollover as long as they are a member.