The kit instructions are very good at detailing how this door is installed but I will give you some tips.
First dry fit your door so make sure it fits. You will have to sand it down on all sides so the door does not snag on itself as you open and close it.
Sand the sides of the door tabs that go into the floor and top unit holes. These tabs are square but they work better rounded and without any sharp sides that will snag as the tabs turn in the holes.
Assemble the top unit as instructed. It basically goes laminated together to form the top door trim but it has two holes for the top door tabs to go into so it can move.
Make sure you have a good door fit before you install the bottom tabs of the door into the porch floor and the top tabs to the top unit. Slide the top unit into the top of the door opening, with the door in place.
Swing the door to make sure it all works and take it out again if it does so you can glue it back in. Make sure to not get glue on the moving parts of the door.
Use spackle both on the door edge and the opening to fill in any gaps in the laminated parts.
Add doorknobs if you wish.
If you can remember the picture of the Lawbre Dollhouse, I am trying to borrow finishes from, pictured on the first day of this assembly blog, then you will remember the stonework on the front facade of the porch foundation.
I had a similar stone pattern printed out, in scale and the right color, and glued it to the front of the porch foundation, recreating the same look. I used tacky glue, sparingly to glue it.
Your stone work does not have to be a printie. You can create it using paperclay, wood, real stone and mortar, stone veneer and even polystyrene plastic stone sheets. You can even stencil your stone look using craft paint. Your imagination is the limit.