ill explain it, the tutorial does a good job if you read it carefully though
a rotating door is like a normal door in alot of ways. but there are two things that are different
1) its a func_door_rotating instead of a normal func_door
and
2) it needs a brush textured with ORIGIN to be part of the door, the center of the brush is the point it will rotate around
make your door brushs, but don't make it a entity yet. then, on the side you want it to rotate, make a square/rectangle that has the texture ORIGIN on all sides, the X in the middle of this brush is the point the door will rotate about. Then select both the ORIGIN brush and the brush(s) that you want to rotate. tie them to a func_door_rotating and set it up. the tutorial should have good info on what most of the things that are neccisary do