If you have played any browser puzzle game before, you already know what to do. If that is not the case, let me explain you how this game works.
So, as you load in each level, you will see a phrase, followed by an image. Basically, you have to use the information given to you to progress in the game.
You input the answers by changing the HTML file name on the URL. All answers are lowercased and without spacing. If your input is correct, you'll be redirected to the next level. Else, you'll end up in a 404 page. The first 10 levels are introductory, so they are easier.
Good luck and have fun!