Tryhackme works on a level system. This is also echoed over into the Discord server - if you're a member of that. Levels are obtained by playing rooms on the website. You will get a certain number of points for each question that you complete. Challenge rooms give more points than walkthrough rooms, and recent rooms give more points still.
You can view your current level on your dashboard:
There are currently 13 obtainable levels:
Title / Level