"AP" stand for Annual Pass, which allows you unlimited access to all the parks for one year. I think that if you plan to go to the parks for 8 or more days, it's a better deal to buy an AP than Parkhoppers. Some people who like to go every year buy them, then schedule their trips one week less than a year apart, making the AP's a good deal. Disney usually has some room discounts for people who have AP's. They only release a certain number of discounted rooms, so you need to call in a timely manner when they are released. Also, only one person in the party needs to have an AP to get the special rate, so sometimes, if the discount is good enough, it pays to buy an AP for just one person, just to get the discounted room rate.
Hope this helps! Welcome to these boards---you can get lots of advice around here, that's for sure!