Click the correct square. If you get it right, the pattern will get longer and you'll have to play it back correctly.
If you get it wrong, the pattern will shorten till you get it right.
Try to get a pattern that's five sounds long!
You can also enable Free Mode with the button above. In this mode, you can make the pattern as long as you want, but you can't make any mistakes, or you'll have to start over.
A bulb () will appear for each sound you get correct. You can use that to keep track of your progress.
If you want to try a different mode later, just refresh the page.