Each key on the keyboard is equivalent to a piano key, although to be able to produce certain sounds you'll have to use a combination of these.
The key's layout can be modified. All you have to do is select the symbol you want to change and the note it will reproduce.
While playing a MIDI file, MidiPiano will highlight the keys you have to press to obtain the same sound you’re hearing. The Demo folder contains some examples that you can play using the program.