If you are replacing an existing door with a unit that was not purchased prehung, you will need to install the hinges and a lockset.
Plan to install the door in stages rather than as one unit.
You will need the door, side and head jambs, hinges, doorstops, a lockset and trim.
You will need to construct and install the jambs, shimming them to make them plumb and square.
After checking for level and nailing the frame into position, cut off the shims flush with the edges of the jamb.
Install the hinges on the door first. Be sure that the door is approximately 1/4-inch narrower than the jamb opening. If you need to trim it, plane or saw the hinge side. The latch side should be beveled.
To be able to where the hinges are to go on the door and the jamb, set the door in place and temporarily shim it to make a 1/8-inch clearance on both sides. Then mark the hinge positions on the jamb and the stile edge of the door.
Usually, the top of the top hinge is 7 inches from the top of the door and the bottom of the bottom hinge is 11 inches from the bottom of the door.
Center the middle hinge between them for exterior doors. Take the door down, and trace each hinge outline on the edge of the door with a sharp pencil or knife, allowing each hinge leaf to extend 1/4-inch beyond the edge of the door so that the knuckle will clear the casing.
Make the knuckle inside, not outside, the house. Using a sharp chisel or router, cut mortises to the thickness of the hinges.
Then screw the hinges to the door, pre-drilling for each screw. Be sure to drill straight holes; if you drive the screw in at an angle it will pull the hinge out of alignment.
Cut mortises in the jamb the same way as for the door, tracing the outlines of each hinge on the jamb and then chiseling out the mortise. A trick to hanging a door is to mark and attach the top hinge first. Screw the top hinge to the jamb, then mark the other hinges and cut them.
It should have about 1/8-inch clearance on each side.
Make adjustments by placing a thin cardboard shim behind a hinge or by deepening the mortise.
Cut the bottom of the door to allow clearance for any carpeting, the threshold, or weather stripping. Use stop material 1 1/8 or 1 3/8-inches wide.
Hold the door closed in it’s proper position, and have a helper trace the outside edge of the door along the jambs with a sharp pencil.
Then measure and cut the stops to length, and nail them with the outside edges on the pencil line.
For greater security, install jamb stock made for exterior doors; the stops are milled as an integral part of the jamb and cannot be pried off.
Install the threshold, lockset, weatherstripping, and trim, using common techniques. You can either paint the door or finish it with a stain or clear finish. Applying a double coat of oil-based sealer will ensure a handsome appearance.