A prehung door simply means that the door is already mounted onto the frame, which will save you all the work of mortising the frame and the door to receive the hinges. The door and the frame are predrilled to receive the knob and strike. If you want to use prehung doors it is great because you can easily do your installation. Just do it correctly and certainly in order to fit it in when opening.
You have to consider also the type of the door you want for your home and because it comes in different sizes and frames, you have to measure and adjust if necessary.You have also need to consider the swing of the door, type of frame you want, the width of the jambs, the bore, exterior doors, and special sizes. You need to ask professionals if you don't have any idea how to detemine these.