Theme folders and purpose:
/activity/
BuddyPress plugin related
/assets/
Theme image, css and js files
/bbpress/
bbPress plugin related
/blogs/
BuddyPress plugin related
/forums/
BuddyPress plugin related
/functions/
Theme functionality files
/groups/
BuddyPress plugin related
/languages/
Theme translations files
/members/
BuddyPress plugin related
/registration/
BuddyPress plugin related
/templates/
Theme display templates for specific post types. Default is post