No, it isn't incredibly simple or very obvious lol, so it's not you. :)
If you want to join a forum, you'll have to find a member of that forum, click/tap on their name, and then go to their profile page (the click/tap will take you there). On their profile page, you should see a widget/module titled "Communities". Next to the community name, you should see "Join". Click/tap on that, and you can join the community.
If you just want to watch a community, and follow what is being posted, you can scroll to the bottom of the topics list (all the posts that others have posted), and click/tap on "Watch this community", and updates will appear on your Watch List.
The Content on this Site is presented in a summary fashion, and is intended to be used for educational and entertainment purposes only. It is not intended to be and should not be interpreted as medical advice or a diagnosis of any health or fitness problem, condition or disease; or a recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action. Med Help International, Inc. is not a medical or healthcare provider and your use of this Site does not create a doctor / patient relationship. We disclaim all responsibility for the professional qualifications and licensing of, and services provided by, any physician or other health providers posting on or otherwise referred to on this Site and/or any Third Party Site. Never disregard the medical advice of your physician or health professional, or delay in seeking such advice, because of something you read on this Site. We offer this Site AS IS and without any warranties. By using this Site you agree to the following Terms and Conditions. If you think you may have a medical emergency, call your physician or 911 immediately.