How do I put MIDI files on my iPod?

iPods will not recognize MIDI Files since they are not "audio files".

However, you can convert MIDI files to audio - mp3 for example - by using the appropriate software (type is commonly known as DAW).  You may want to edit the files first to remove unneeded parts, change sounds, change keys, etc.  Usually, the same software can do the trick, or you can use any MIDI sequencing program.