Maybe you tried to use DEF like Function in VBA...?
To return a value, you need to write RETURN value instead of FunctionName=value.
Also, you have to add () to the function name, if it returns one value.
ACLS DEF APRS() 'CHECK IF A PRESSED IF BUTTON(1,#B_RRIGHT)==1 THEN RETURN 1 RETURN 0 END LOOP 'INITIAL GAME LOOP FOR TESTING STARTG VSYNC ENDLOOP DEF STARTG 'COMMAND TO DISPLAY INITIAL TEXT CLS LOCATE 10,3 SPSET 0,2 SPOFS 0,192,112 PRINT "WELCOME, PRESS A TO BEGIN." IF APRS()==1 THEN PRINT "CHERRY" 'JUST TESTING WHETHER IT RECOGNIZES THE INPUT END