If you want to create your own private projects and sessions you will need a private account. If you don't need to create your own private projects and session, but you want to participate in private projects and sessions, you will want an access account. If you only want to participate in public projects and sessions, and you don't need to create your own private projects and sessions nor participate in other users'private projects and sessions, you will only need a free account. You can upgrade your account at anytime if you find you need greater access, to create private projects and sessions, or more storage and bandwidth.