A series is a coach's multi-week program — a 6-week clinic, a season-long plan — made up of an ordered sequence of classes and self-practice drill sessions. Your coach enrolls you in the series itself, which is a separate step from being enrolled in each individual class inside it, so check that you're on the roster for both the series and the specific classes you expect to attend.
Like everything else, a series (and each item inside it) only shows up for you once published — see Draft vs. published: how content becomes visible. Once published, you'll see the full program: its date range and the ordered list of classes and sessions that make it up, so you know what's coming next.
Available to all users, including students.