As soon as the the screen starts you are given a quadratic expression to factorise (factor). In at the deep end!
If you're not sure how to go about it, try moving the four sliders at the bottom of the page with your mouse (click-and-drag) to see what happens. The answer will be of the form (Ax + B) (Cx + D), where A, B, C and D can be altered using the sliders, and 'x' is the variable (it might be any letter).

When you have the right answer you'll be told. You can then press "New Problem" and have another go.
If you click in the box labelled "Easier" at the top right, you get some slightly easier questions, where the coefficient of x² is always a prime number. You can make the questions harder again by clicking the box again to remove the tick.
Play around, and watch carefully what's going on. You'll soon be good at this tricky but important skill.