Step 1. Assemble
Lay the door frame on a flat surface and then sit the door into the door frame rebate.
Make sure that the gap between the door and door frame is even all the way around.
Screw two hinges to the door and the door frame: one at the top and one at the bottom.
Use either butt hinges or T-hinges.

With the door still laying on a flat surface fix 75mm x 25mm (1x3) trim to the perimeter of the door frame.

Step 2. Install
Place the completed door and frame into the door hole (rough opening) in the wall. Ensure that the door is level and plumb and that the gap between the door and frame is even all the way around. Then fix it in place by nailing through the trim into the wall.

From inside the room, nail the door frame side jambs to the wall rough opening frame.
Because the rough opening will be (or should be) slightly bigger than the door frame, packing pieces will need to be placed between the jamb and the wall frame where nailing occurs.

Usually the door frame is of an exact width so that the inside of the window frame will be flush with the inside of the wall allowing for a molding, architrave or casing to go neatly around the frame.
However......
in this case the door frame is wider than the wall and therefore projects in to the room.
Finish by fixing a 25mm x 25mm (1x1) square bead (piece of wood) around the perimeter of the door frame to the wall.

Fit hardware of choice: in this case we've used D handles and a roller catch so the door can always be easily pushed open.

Safety Tip!
How to help prevent little fingers from being jammed by a door.

This particular door is likely to be more of a risk to little fingers than a normal house door because it is a lot narrower than a normal door making it easier for a child to reach the hinge side of the door, and also because the door is a playhouse door, it is always going to be surrounded by kids. Big kids should not be of concern, it is more for the little kids, crawlers and toddlers that may need a bit of "finger protection".

Click here for instructions on how to help prevent little fingers from being jammed by a door.