Measure the door opening width, height, and wall thickness
Cut the jamb legs to the required height
Cut the head jamb to the required width
Mark and cut the hinge mortises on the hinge-side jamb leg
Mark and cut the strike plate mortise on the latch-side jamb leg
Assemble the jamb pieces into a U-shape
Check for square by measuring diagonals
Clamp the jamb and adjust until square
Fasten the jamb joints with nails, screws, or wood glue as needed
Install the jamb into the rough opening
Shim the jamb plumb, level, and square
Secure the jamb to the framing with fasteners
Trim any excess shim material
Verify the door fits and swings properly