how do I write line 9 so that if someone presses the A button, the screen clears and the sequence restarts?

If button (0) and 16 then ... The first number in button is the feature, such as repeat. The second number is not needed unless you have multiplayer. Button will equal a number when that button is pressed, like 16 (a), 1(up). You can also use the # numbers. Like #up, #a

ok thanks

If you want to compact it a bit, some ways to do that include declaring a variable (BTN for example) that is equal to BUTTON(0), and you don't need the AND either. IF BUTTON(0)==16 does the same thing. Whatever you want to do though! ;)