Elevator (Portal 2)
Elevators are a function used in Portal 2 to transition the player from level to level. Not to be confused with the Disassembler, which took the players from level to level in multiplayer.
Step 1: Select the entity tool and create a func_instance and give it the name "Arrival_Elevator" and choose the VMF file name "instances/turbine_elevator/arrival_elevator_a4_base.vmf"

Step 2: To make things simpler, and to not have to create 2 func_instances and find the second one through all this mess, simply Shift+drag the "Arrival_Elevator" one unit to the left, right, up, or down to copy the first func_instance, and quickly put the copy exactly back on top of the original.(Note: This step is crucial as the two func_instances MUST be aligned directly on top of each other.)

Step 3: Double-click either one and change the name to "Arrival_Logic" with the VMF file name "instances/turbine_elevator/arrival_elevator_a4_logic.vmf"
Step 4: Create one more func_instance entity anywhere, I prefer to put mine right behind the elevator model(Note: do not put it inside elevator model), name this one "Arrival_Departure_Trans" with the VMF file name "instances/transitions/arrival_departure_transition_ents.vmf"
Step 5: Your elevator is almost complete, now you will notice that at the middle of it, is a hallway looking extension. This is the hall where you will spawn into, you must seal off the "NoDraw" texture surrounding the hallway or the map will show a leak!(Note: You do not have to box the entire elevator, just seal off the NoDraw at around the exit hallway.)

Now your elevator is complete, congratulations!