Installing the door into the opening & attaching it to the hinge pins. Slide the door back into its spot from the inside of the building making sure the indentations for the pins are lined up. Put some glue on the trim piece & install it onto the front of the door. You may have to wrap a piece of clear tape around the door to make sure the trim stays in place until the glue can dry.
You want to make sure this glue connection is strong because the door is going to pivot on those pins to open & close. Be careful not to put too much glue right on the hinge pins because your door may end up glued in the closed position.
Do this same procedure for the garage doors I left the doors taped together through the whole process to make sure everything stayed lined up. Once everything is completely dry take the tape off the doors & make sure they move freely, if not lightly sand where needed or use your utility knife to do any minor trimming. Be careful when trimming or sanding so you don’t tweak the doors.
This is actually a fairly easy way to make doors that open & close, they should work properly for years. When displaying you can leave them in the open or closed position or have them half way open whatever you like. If you decide to put a light in your diorama building you may want to leave them open just a crack so the light shines through the opening for an interesting effect.