You can either create your own account and password (you don't need a real email to sign up).
Or, you can log into any of our existing users. For instance, to log into the 'Alice' account you can use the email 'alice@alice' and the password 'alice'
Under the 'Groups' menu tab, you can see all the posts made by members of different groups. Each one of your group memberships will have a different tab. Simiarly, the 'friends' tab will allow you to see the posts made by each account you are friends with.
In addition to viewing posts from friends and groups, a user can also add posts, and like them, and search for existing posts using the search fields. This functionality is relatively self-explanitory for people familiar with navigating social media. Lastly, a user can choose to delete his or her account, and doing so immediatly deletes all their friendships, posts, group-memberships and all groups that they are registered as the owner of.