Later tracks unlock as you reach new stages.
Tracks unlock as your stage goes up, so you build the basics before the advanced work. By default the Intermediate track unlocks when you reach the Intermediate stage (500 points) and the Advanced track unlocks at the Advanced stage (1,500 points).
The quickest way to unlock the next track is to keep finishing lessons in the track you are on. The shorter courses (Reviews, Compliance, Email) are open from day one.
Related: Stages, How points work