If you are a member of a Missing Link dojo, your licence for the community will have been handled for you. Your teacher will sort out your Student Circle Membership (or a higher membership, depending on which level you are at). You can request your username and password for the Online Resources on this site from them. 

If you are an independent Karateka or martial artist wanting to join the community, you can apply here. It's a very simple process, and a licence entitles you to access to the Online Resources, but more important you can attend Missing Link gradings and receive discounts for seminars and workshops.