I brought this up as well....I think MH should bring back the clearly visible "join community" button.It took me a LONG while to figure it out recently. Plus, you don't always need to ask a question, but may want to be a part of a community, or, you may wish to ask a question once, but not necessarily join. I don't care for the way this is done...very non user friendly, IMO.
Hi there -
When you post a question, you will be added to that Community. The other way you can join is to find a member of that Community, click on their name to take you to their profile, and then click "join" from their Communities List.
Let us know if you have further questions.
Emily