How do I start using Looking for Group?

From the guide. Press the Xbox button to open the guide, and then select Multiplayer > Looking for Group.
From game hub. Highlight an item, press the Menu button on your controller, select Game hub, and then select the Multiplayer tab.
From a club that you’re a member of. Press the Xbox button to open the guide, select People > Clubs, choose a club from the list, choose the Multiplayer tab, and then select Looking for Group.
From a club that you’re visiting. Press the Xbox button to open the guide, select Home, select the Community tab, and then select Clubs on Xbox. Browse the featured clubs or search by selecting Find a club. Select a club, and then select the Looking for Group tab.

To use Looking for Group, you might need to change your privacy settings.

Press the Xbox button to open the guide, and then select System > Settings.
Select Account > Privacy & online safety.
Select Xbox Live privacy > View details & customize > Communication & multiplayer.
Under Others can communicate with voice, text, or invites, select Everybody.