The Groups tab will display the list of groups that you are part of and all the open and closed groups that are in the spot but you are not a part of it yet. You will not find any private group in your group list as these are hidden groups.
To join a feed group, follow the steps below:
1. Go to Groups and click on the Join button to become a part of the open group
You will now have access to the group
1. Go to Groups and click on the Request Join button to become a part of the closed group Once the admin has approved your join request, you will have access to the closed group