I'm surprised no one sent him here yet:
Read through those. Guaranteed you'll find what you're looking for.
Your just starting out so you need to do some reading first....but the one piece of advice that I will give you is don't let people talk you into wasting money on unnecessary hardware.
The $10 ELM-327 units from ebay work just as well as the $100 OBD-II readers people might suggest for anything you might use them for.
I have a 2000 Jeep Cherokee Sport.
looking into the ELM-327 units now and doing some further reading.