There's a very good intro to MIDI here:
http://tweakheadz.com/how-to-get-sta...ording-studio/
Done humourously and lightly, but with good information.
The Midi Association has a how-to here:
https://www.midi.org/articles/an-intro-to-midi
Amazon features a number of books on midi. Here's a link to one of them:
http://www.amazon.com/The-MIDI-Manua.../dp/0240807987
And our own Sherry Crann has put together a number of tutorials on getting started and using Notation productions that includes setting up and using midi keyboards here:
http://www.notation.com/TutorialVideos.php
Hope that helps.
David