BuddyPress.org

@amahesh – You need to wrap the code in functions.php with open and closing PHP tags.
eg.

Replace square brackets with triangular ones.

@amahesh – You shouldn’t be modifying any files in /plugins/buddypress. If you’re modifying the bp-default theme, build a child theme . That way, when you upgrade BP, your changes will not be wiped out! Once you build your child theme, follow the instructions I outlined above. And yes, you make a duplicate of bp-activity-group-feed.php and put it…[Read more]

@amahesh – In your theme’s functions.php, make sure your code looks something like this: http://pastebin.com/Pn1jFXG5 Read the comments in the code. Then In your duplicate of bp-activity-group-feed.php, you need to change: if ( bp_has_activities( 'object=' . $bp->groups->id . '&primary_id=' . $bp->groups->current_group->id .…[Read more]

@amahesh

You will need plugin
https://buddypress.org/community/groups/buddypress-announce-group/

@amahesh Set the group to private group and it will require approval first before become member