Go to the storefront of the provider you want to book the class from and log in if you haven't yet.
On the Activities tab, find the activity you want and click on Join.
On the Redeem section, you can choose the plan you want to use if you have more than one. If you don't have a plan, you can purchase it as pay as you go.
If you haven't added a payment method, you will be asked to add one.
Click on Complete.