It's pretty straightforward. Each Level has videos, documentation and challenges that you need to complete. The goal of the videos is to model and show you how to use a tool, while the challenges give you an opportunity to practice. Note that you must complete Level 1 before you can move on to Level 2, and Level 2 before Level 3. 

Once you pass the certification test for a particular level, you will receive an email containing a certificate and a badge. This will signify your successful completion of the level and you will be able to move on to the next level.