SoM Online Covens;
SoM has a variety of "covens" to chose from, one of the covens you can join is "Spell Casters", this coven when you join places anyone into "Council" position. Council members have the ability to place articles and spells onto the "coven" article and spell book pages.
Now if you want to get into a coven that has a Priest, Priestess, or both in it, most of them require your to fill out some sort of form and send it to the Priest, Priestess, and sometimes they prefer to send to them both. After they have time to think it over they will either accept or decline your request, not remember before or after you send the form, you must gointo the link that says "Accepting Applications" and click the "Send Application" or something like that. Otherwise they can't accept your request or decline it.
Now when chosing a coven, I'd suggest reading through all the covens before chose the one you want. Remember each coven is different. Once you found the coven you like do the instructions above. Fill out form truthfully. Don't lie because that could get you into trouble by the leader(s).
Real Life Covens
Now in joininig real life covens, most covens don't allow minors (people who are not 18+). Most covens request adults to be apart of it because of their maturity. Some covens may be into more adult magick (such as blood magick, sacrifising..ect) those things can get them into trouble if a minor is doing them. Now joining a real life coven is harder then joining a "Online" coven. This is because they have more tests and probably a few that require a physical work.
Even though being apart of a coven is fun, there is always coven loyalty that you have to remember, keep what is discussed between coven inside the coven. Unless the Priest or Priestess tell you otherwise.
Now coven creation, now orginizing your coven isn't easy and will never be. There is making your coven and being able to operate it. Choosing your members are not easy either. Once you start getting application to be apart of your coven, then you will start having to use your instincts this is because there could always be fakes trying to get into your coven.
Now make also sure that the people you get are age appropriate if you are planning on doing adult rated stuff, and actually do research on the topics your want to discuss, this is because a lot of people misinform their members and they go off tell others.