By default M2tklib supports aktive low push buttons: Connect an Arduino pin to a push button and the other end of the push button to ground.
A keypad can be used, but you need to define your own "event source", which is not really described at the moment. Let me know if your really want to use your keypad. In this case we need to study the datasheet for the keypad and write a specific event source.
Another way is to simulate input by using the serial monitor.
With the serial monitor you can test your menus without extra input hardware. Instead, input on the serial monitor is used to navigate through the menues. For example look at the Combo.pde:
You will find the following line:
M2tk m2(&list_element, m2_es_arduino, m2_eh_2bs, m2_gh_lc);
Add "_serial" to the event source:
M2tk m2(&list_element, m2_es_arduino_serial, m2_eh_2bs, m2_gh_lc);
This enables the serial monitor to navigate through the menu. Remember to activate the serial monitor in your Arduino IDE.
This can be done for all examples, and of course it might be a good starting point for your projects, if you have not yet decided which hardware buttons to use.
Looking at the examples is a good starting point. And it seems that the examples are already working (I am glad the M2tklib works in your environment). I also suggest to look at the first three tutorials:
Tutorial 1: General setup
Tutorial 2: How to apply the above mentioned push buttons
Tutorial 3: How to build a simple menu/dialog
I also suggest to read
Tutorial 7: How to use the serial monitor interface
as mentioned above for quick success without additional input hardware