Basically MIDI references notes on a range from 0 to 127. With 12 notes per octave, that gives you an impressive range of over 10 octaves. We've only taken advantage of a portion of MIDI's maximum potential. Using the various other control surfaces on your keyboard like a ribbon controller, pitch bender, data slider or mod wheel will also send MIDI data that can be recorded on your sequencer. These types of events are called controllers , and they basically alter one parameter of the current instrument's sound.
Pitch bend obviously alters the pitch of the note, the mod wheel often adds a vibrato effect.
Synths also commonly have data sliders and ribbon controllers that can be set to alter volume, panning or effects levels amongst other things. It is usually very open ended, allowing you to control any parameter you desire. Again, you'll need the manuals for your gear to see what controllers are recognized, and also how to configure your control surfaces to transmit the controller number that you desire. Another parameter you'll be interested in is the velocity of the note. Like most MIDI data, it's a number in the range of 0 to 127, and it corresponds to how hard you pressed the key on the keyboard.