You can offer your academy free or paid. To charge, you connect your Stripe account (Stripe Connect): your students' money goes into YOUR Stripe account, not Onyx's.
Payments are processed by Stripe. Onyx applies a platform fee on sales (you see the percentage in your panel). Stripe's fees and that fee are deducted automatically; the rest lands in your Stripe.
You can turn on an affiliate program: your students share their link and earn a commission for every subscriber they bring. You set the percentage and see pending and paid amounts in your panel.
When a student finishes a course, they get a certificate with YOUR academy's name.