RTF means ready to fly - usually a plane kit that comes with all the electronics, battery, motor, radio control, etc so that you can fly right outta the box
CG means center of gravity - it's like a balance issue, if people say that the "CG" should be 4 inches from the nose then you would balance the plane on something where it would sit 4 inches from the nose and you would add wieght or move parts around so that the plane kinda sits there without falling over too much to the tail or nose...lol does that make sense? My Slo-V (slow stick) had a CG like 3 inches or something from the nose, so I'd move my wing back and forth a bit to the right spot where it would appeared to be "balanced" when I held it 3 inches from the nose.
That being said, the flight programs are pretty darn good, don't be afraiid to crash either, I mean you'll never learn unless you try - one thing to keep in mind when you fly for the first few times is to try and get some altitude so that if I make a wrong turn I have time to correct myself before crashing
Good luck man, and happy new year!