Where is the completed or submit button for registration?

Hello! I'm not sure exactly what you're trying to do, so here are a couple possible solutions:

Manually adding students--

People > Students > Add student (at the bottom of the page)

Public page method--

Promote > Publish (skip if already published) > View > Register > Add student (at the bottom of the page)

I hope that helps you. If you need further assistance, please provide more details. Thanks!