There's a lot of books on the market regarding MIDI.
One basic suggestion is an old book issued by Keyboard Magazine which gives the basic concepts of MIDI and includes the MIDI standard. The title is something close to "Synthezizers and Computers"
What you could do or not with your RD600 is referred in the MIDI implementation chart table listed in the RD600's users manual.
The referred book explains the use of the informations on the table.
It's not quite simple for a beginner, but as time goes by you will notice that is possible to get it.
To use your PC with low budget, you may connect it to the RD600 by a Sound Blaster Card (any model) and a MIDI cable exclusive to that card (it does NOT match the MIDI standard, so a regular MIDI cable will not serve)