If it came with the harness for your car, then it should just hook straight up, without having to worry about what wire connects to what wire. If you only got the deck harness, then I would strongly recommened going back to that store, and ask for "harness adaptor kit" for your car. Usually about 5$ and it will save you a lot of time and hassle. One end would hook up to the deck, and the other end would hook up directly to the cars wiring harness.
The other thing you might want to look at buying is a "mounting kit" - if the stock deck in the car was (and probably is) bigger then the new cd player, then the cd player is going to just sit there...very easy to steal at that point. The mounting kit will make the install look a lot cleaner, and they only cost you a couple bucks as well, and make things a lot more difficult for would be thieves.
But, if you want to just wire it in the way you want to....
1) There would be a chart on the stock deck, and probably a wiring guide in the manual of the new deck. 1+1 = 2....
2) It only requires one line for power....but there should be a grounding strap that was attached to the stock deck, and there should be a hole on the back of the new deck that you can attach it to as well.
3) Accessory is for when you turn the key to the "accessory" position - it allows the deck to get power without having the car running... Generally yellow wires - should be one there for the stock deck as well.