1) Please ensure you have installed and activated the BuddyPress and bbPress plugins.

2) Go to Settings -> BuddyPress and click the Components tabs and enable "User Groups" and any other features you want to use.

3) Next click the Pages tab and ensure that each dropdown menu has a page selected - if a dropdown menu is empty either create a new page or select an existing page. You do not need to add anything to pages - just leave them empty.

4) If you imported the demo data the links to the BuddyPress pages may need to be edited. Go to Appearance > Menus, find the menu with the BuddyPress links and delete them and replace them with the correct pages.