Well, there isn't really a concrete concept or implementation of a menu. A menu can be anything that offers options to the user in order to do something.
A simple implementation for a menu can be a limited number of options, where one of them is currently selected and you can change the selection through some method.
You could then finalize the selection by some method, and the program would continue depending on the selected option.
For example, having 3 options "GAME A", "GAME B" and "EXIT", you could print them on screen. Your selection would be determined by a variable SLCT. You'd change this variable using BUTTON. You'd draw an arrow on screen depending on this variable to show what option is selected.
You could then finalize selection with BUTTON again. You would The example would look like this...
REPEAT
PRINT " GAME A"
PRINT " GAME B"
PRINT " EXIT"
LOCATE 0,SLCT
PRINT ">"
B=BUTTON(2)
IF B AND #DOWN THEN
INC SLCT:IF SLCT>2 THEN SLCT=0
ELSEIF B AND #UP THEN
DEC SLCT:IF SLCT<0 THEN SLCT=2
ENDIF
WAIT 1:CLS
UNTIL B AND #A
Sorry! Ignore the incomplete "You would" in my previous comment. I meant to say you should wrap the menu code in a loop, like I did.
After a selection is made (by pressing A), you'll get out of the loop and SLCT will tell you what option was selected. This way you could have a branching conditional, like this...
IF SLCT==0 THEN
'GAME A
ELSEIF SLCT==1 THEN
'GAME B
ELSE
'EXIT
END
ENDIF
