Re: The requested URL /register/ was not found on this server.
Run Settings > Permalinks and set to other than default i.e. pretty permalinks is a must. Double-check WP configurations and if you have a problem there, resolve it in WordPress.org forums before installing BuddyPress.
https://codex.buddypress.org/getting-started/before-installing/
https://wordpress.org/support/
You do not move BuddyPress plugin folder/files around in your server at all. You can install BP in either of these two ways:
1. auto install via dashboard menu Plugins > Add New > BuddyPress then network activate. or
2. Upload buddypress plugin in wp-content/plugins/ folder in your server, then go to dashboard to activate BP
After either #1 or #2 above, Install a BP-compatible theme like https://buddypress.org/extend/themes/ and you’re good to go.
