Depends on what you want to do. Right now you haven't fed in any instructions on what it should do when a button is pressed. So if I were SmileBasic and you pressed A, I would read your line 9 then go to line 25 and 26, which tells me to go back to line 3 where your loop is. I'd be doing 9->25->26->3->9->25->26->9... infinitely WITHOUT showing any work. The result is nothing but a blank screen.
Try something like this. If you press UP, it'll print a corresponding message. The VSYNC 1 is important because SmileBasic is so fast, you don't want it to flood you with the printed messages. I leave you to compare BUTTON() with BUTTON(3). Finally the green text below the diamonds is a simpler code that does the exact same thing.
The Start button (nor the Select button) can't be read in a SmileBasic program.
The other buttons' numbers have constants assigned to them. Some examples: #A, #UP, #LEFT. If you use the constants, your code will be more readable.