BuddyPress.org

@jhansensd http://testbp.org/ has the default theme and your users don’t have to go to the backend to log in. As for registration, it’s the “Create an account” in same login panel on the sidebar. You can can easily create a Register Now button in your BP child theme if you prefer. Users do not install bbPress, the Site Admin does.

Recommend that you read the “Getting Started” section in Codex – https://codex.buddypress.org/home/