Tracks can be completed in two modes on Exercism - Mentored Mode and Practice Mode. You can choose a different mode for each track.
Mentored Mode gives you the full Exercism experience. The track progresses in a structured manner, teaching you a new skill with each exercise. Every time you submit a solution, a mentor will give you feedback and advice on how to improve your code. Once you've made a little progress, they'll approve your solution and you can unlock the next step in the track.
Every time you complete a solution, you'll also unlock extra bonus exercises. These are designed to give you opportunities to practice what you've learnt so far. There are lots of bonus exercises so you should always have some new challenges to be getting on with while you're waiting for our mentors to review your exercises.
We try to respond to all core submissions within 24hrs, but as our mentors are volunteers helping in their evenings and weekends, we can't guarantee that we will hit that goal. Our bonus exercises hopefully mean you won't get frustrated waiting for feedback :)
We designed Practice Mode for people who want to take fast, deep-dives into a language without waiting for mentor feedback. In Practice Mode you can take the exercises in whatever order you want and there is no progression or unlocking. You may request mentoring on one exercise at a time, but your solutions will have a lower priority than people in Mentored Mode.
Changing mode on a track
While we recommend sticking to one mode per track, it is possible to change if you decide you've made the wrong decision. You will find the button in the "Danger Zone" section of a track page, which is on the right-hand-side in Mentored Mode and the bottom of the page in Practice Mode.
Some tracks are oversubscribed, meaning there are too many students per mentor. In this situation, anyone starting the track is forced to start in Practice Mode, and no-one in Practice Mode will be able to request mentor help until the track is back in a "healthy" state. At the time of writing, we define an oversubscribed track as one that has a median wait time of over one week.