In the following tutorial we create a rotating door in L4D hammer, complete with sound and coolness.
1. Create a frame where you door will go.
2. Place an entity called 'prop_door_rotate'
3. Double click on the entity to go into object_properties.
Click on World Model and select the door you want by typing in door in the filter section.
4. Position the door into your door frame and you may need to resize your door frame brushes to match the door.
5. Double Click on the door to view the properites. Under sound you will add
Click on Browse for each and select appropriate sound for your door.