To use the buttons as a part of a functional menu you simply need to have the function, that handle the press for that button, call a function that will redraw the screen with the buttons (and anything else you need) for the selected menu option.
Note that you may need to save some information about the menu screen before you do the redraw. You may also need to set some flags so your main loop knows that the selected option is active and it's safe to call other functions (like processing presses for new buttons) for the new screen)
Also note that you may want to save info from the selected option before you go back to the menu screen