You have to close a door before you can open it.
If you stand in front of a door and the door opens towards you
and the hinges (or at least the hinge pivots) are on your side of the wall
and the hinges are on the right then it is a DIN standard right opening door.
If you can see the hinges on the left then it is a DIN standard left opening door.
If the hinges are in the middle and the door opens in both directions
then it is a funny opening door.
Doors are a useful invention that let you go through walls.
If you take a door off its hinges, it is unhinged, like some people you know.
If you screw four short legs on to a door, unhinge it and place it horizontally on the floor, you will either later trip over the legs or you will have a large coffee table.
You cannot ski through revolving doors.
You have to open a door before you can close it.