Fight Lab is a sort of tutorial or intro if you will intro the mechanics of Tekken. You take control of Combot and learn various things about the controls and moves of the Tekken universe wrapped around an amusing story. There are five stages to Fight Lab and each of them has three chapters: An introduction into what you are about to do, a phase of doing it, and then a boss battle. While doing these you earn points to upgrade Combot for the Super Combot DX Complete achievement. You also gain fight money along the way which helps towards theBazillionaire achievement.
The various achievements relating to Fight Lab will pop up at the end of their respective chapters.