By first selecting the face where I wanted the door to go and using the extrude tool,
I could then adjust the size of the face which I would then extrude back to make a hole.
I did the same on the reverse of the door.
I then extruded backwards into the door and deleted the front face
I then deleted the faces of the extrusion I had just made, this left me with
a hole in the door.
Putting a door into the hole.
I simply made a new polygon cube and scaled it to the size of the hole.
Now that the door is made and in the hole I now need to put the door onto
a different layer to make things easier.
This is simply done by selecting the object and then clicking the icon shown here.
