As soon as the the screen starts you are given a quadratic expression to factorise. In at the deep end!
If you're not sure how to go about it, try moving the two sliders at the bottom of the page with your mouse (click-and-drag) to see what happens. In the box on the left you should see a multiplication being done on the values you have entered, and on the right is your progress towards the answer.
You can start with easier questions by clicking the box labelled "Positive values only". You can move on from there when you are ready by clicking again and unchecking that box.

When you have the right answer you'll be told. You can then press "New Problem" and have another go.
You can show or hide the working by checking or unchecking the "Show the working" box at the bottom.
Play around, and watch carefully what's going on. You'll soon be good at this important skill.