If you can’t find the menu item “Communities” in the action bar directly under “Home” and “#Discover”, you must first join an open community to activate the new function – for example, the said train driver meeting. For communities with open membership, all you have to do is tap or click on the “Join” button, which is located at the top of each community page under the large community profile picture.
Twitter wants to make exciting communities known
Otherwise, a community invitation from the moderator or another member of the respective community is required. Then you can post, like or comment as usual. Although community tweets do not appear in the “normal” home timelines of Twitter followers, they remain partially public in the community timeline.
All information about the communities, including how to create an affinity group yourself and become an admin, can be found in the Twitter help section. Twitter regularly wants to introduce existing and new communities on its own account.