I assume that by buttons you mean normally open momentary switches.
I use hardware debounce on my button switches. A 0.1uf cap across the switch and that is it. If the 0.1uf cap doesn't debounce the switch properly the switch goes in the trash. I always wire my switches from input to ground with the internal pullup enabled.
I don't know how Mr. Christensen intended that it be used (he is a member here), but if I were using this library, I would declare 4 buttons, then put them in to an array.
Actually I never use a button library, but that is political, so ...