How to hang an internal door.

First, catch your door.  Obviously, the size will be determined by your doorframe. This will roughly correspond to one of the following standard sizes: 78" x 27"; 78" x 30"; 78" x 33".  There are other sizes available from proper timber  merchants and door manufacturers, but these are the most common. Having got a door, this is the order of actions to fit it:

Alter the size; Bevel the edges; Let-in the hinges; Fit the latch and handle; Fit the striking plate.

Bringing the door to size. Don't think for a moment that you won't have to alter the door for it to fit in your frame. Even if the frame is 6mm bigger than the door, once you hang it on the hinges the leading edge of the door will hit the front of the frame as it closes. You have to put a slight bevel on the edge of the door to prevent this happening.