MIDI files can be thought of as digital sheet music. They contain information about a musical performance, such as what notes to play and how loud to play the notes, what instruments to use and so on. They don’t contain fingering advice; the robot performs a search algorithm to decide what fingers to use.
This software can be used with any MIDI file (except extremely rare type 2 MIDI files), regardless of how many tracks, channels and instruments it contains. All notes for all instruments will be played on the piano. The only exception is that percussion sounds are ignored.
The pianist behaves most like a human given sequences of notes that a human could play, such as in a MIDI file of a piano sonata; when an unreachably large span of notes must be played in a short duration the robot’s hands end up moving extremely quickly back and forth or ignoring some notes.
The software comes with no MIDI files. There are plenty of online repositories that distribute MIDI files in all genres, many of which are free. MIDI files exist for a huge number of popular pieces as well as classical.
There are also many ways to create your own MIDI files, such as by recording your own performance using the built in features of many electronic keyboards.