Look it up on YouTube. I'm sure theirs videos out there that can better help you. I use it all the time.

YouTube

The folks at BestBuy will help you out and answer your questions while showing you how to hook up your new stereo. Just make sure you ask the Auto Stereo Installers. they know what they are talking about.

Not difficult, but if you're new at this, there are plenty of You Tube videos on the subject. You may be able to find one specific for your make and model. Remember to always disconnect the battery!

Be prepared for a decent time investment. 1-4 hours depending on your experience level with electronics. The hardest part is wire matching between stock models and aftermarket, but guides and plentiful online for the diagrams. Also make sure you have all of the appropriate tools before you start. Some stereo models require a small crowbar like wedge for removal and installation. Wire strippers with an appropriate gauge for wire size, wire connectors so you don't have to mess with electrical tape, and zip ties to make sure everything can be placed correctly without being damaged.
It shouldn't be to difficult for a first timer, and the satisfaction of doing it yourself makes it that much better.