Every member that joins your portal automatically gets a basic membership. This means they have access to your portal, their personal profile, a few training plans and a few exercises.
With a PRO-membership, they have access to the nutrition app, the body metrics module, all the training plans and all exercises. As a manager in your portal, you decide who gets a PRO-membership. You can decide to make all members PRO, but you can also decide to generate a little extra income by upselling the membership to your clients. This decision is up to you, there are in no way extra costs from Virtuagym to pay.
You can coach clients when they have a basic membership, but they won't be able to play the PRO-exercises or check their progress in the body metrics app. They also won't be able to access the nutrition diary (but you can create a nutrition plan for them).