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Go to https://www.facebook.com/. This will open your Facebook News Feed if you're logged into Facebook. If you aren't logged in, first enter you email address (or phone number) and password in the top-right side of the page. This arrow is in the top-right side of the Facebook page. A drop-down menu will appear. It's near the middle of the drop-down menu. Doing so opens the Discovered tab of the Groups page. All groups on the Discovered tab are tailored for you based on your friends' activity and your current interests.  You can click + Join to the right of a group here to request to join the group. If you'd rather look at groups you're currently a part of, click the Groups tab in the upper-left corner of this page instead. Click the search bar at the top of the Facebook page, then type in a group's name or a keyword and press ↵ Enter. For example, if you wanted to find groups that focus on clean eating, you might type "healthy eating" into the search bar. It's at the top of the search page, just below the blue Facebook ribbon. This will show you only groups that match your search term. Click on the name of a group that looks interesting. This will open the group's page and allow you to view the posts in it if the group is public.  If the group is closed, you won't be able to view the posts. You cannot find a secret group without being invited by a group member. It's below the group's profile picture. This will send a join request to the group administrator. If you're accepted into the group, you'll be able to post and comment on other group members' posts.
Open Facebook. Click . Click Manage Groups. Scroll through the recommended groups. Search for a group by name. Click the Groups tab. Select a group. Click + Join Group.