It's easy to have a bad time with LCD shield as the pinouts vary a bit but, if you have that sorted, I think it is just a matter of the buttons.
I believe the buttons are always on pin A0, and it probably isn't a good idea to use A0 for anything else. You should see in your loop something like
adc_key_in = analogRead(0); // read the value on A0
key = get_key(adc_key_in); // convert into key press
and then a subroutine, possibly called get_key, which assigns a number to the value obtained, and I believe that is where your menu stuff goes.