If you press the blue EDIT button on the keyboard in the bottom left corner, you'll switch to edit mode. This is where you can write code to run with the START button.
Try writing this code:
INPUT "What's your name?",N$
PRINT "Hello, ";N$
Then press START to run the code.
This code will ask for your name and repeat it back to you.
INPUT shows a message and saves whatever you type to N$ and
PRINT shows a message and the name you typed.
You just made your first(?) program! Of course, there's much more you can do with SmileBASIC. Ex: if you wanted to fill the screen with a message, you just need to put this code into the editor:
WHILE TRUE
PRINT "message! ";
WEND
This will constantly put "Message!" on the screen.
WHILE and WEND are the start and end of a WHILE loop. WHILE takes a condition to check every time it repeats, but TRUE just makes it repeat forever.
But wait: how do you stop a program stuck in an infinite loop?! Just use the START button again.
If you want to save a program you made, just hold down L (or R) and tap SAVE.
Hope this helped!