could you tell me what is a preferred room and do I want to "buy" that?
"Preferred" can mean different things at different resorts. Generally, though, it means that you pay extra for a room that's close to the main building, where the main pool, food, and bus stops may be located.
Just to clarify what's been discussed here...
At most resorts, there are several room categories that can be booked. Examples might be a bunk-bed room at WL, a MK view room at CR, or a water-view room at POFQ. Or, a preferred room at Pop. If you want one of these sorts of rooms, which cost more than the standard rooms at these resorts, you need to specifically book that room category. For instance, you can't just request a water view room at POFQ - if you want that type of room, you have to book it.
What the posters are talking about here are more general requests.....wanting a room near a pool. Or a room on a higher floor. For this sort of thing, you simply call CRO (or have your
travel agent call), and have them record your request on your reservation.
The difference is, if you book and pay for an MK view room at CR, you are guaranteed to get one. If you request a room near the pool at POR, they'll do their best to put you there, but it's not guaranteed.