American_4275 is correct as where the aircraft's registration number is concerned. It is on the fuselage, near the tail.
If you're interested in investigating the aircraft's specifications and/or history, a few good sites are
- first of all, http://www.bird.ch/bharms
- it helps if you know the type of aircraft you're looking for, and it will have to be either Airbus, Boeing, McDonnell Douglas, or L-1011.
- secondly, http://www.intercpt.demon.co.uk/fleets.html
is rather nice, although unfortunately, it's not very up to date. Nevertheless, it's a good starting point if all you have to go by for starters, are the airline and registration number.
I hope that helps a bit. I think these sites will provide you with plenty of fun, browsing through them for the time being.
Enjoy, and... welcome!