Step 1: Add Pistons & Door Istelf

First, place 2 pistons on top of one another both facing the same direction. Then, add another 2 pistons on top of one another 4 blocks away from the previous 2 we placed earlier.

Next, add the 2 by 2 square door that you want in-between the pistons.

(Look at the picture above to se if you placed them correctly!)

Step 2: Create On/Off Switch or Button

Next, place a lever or a button so that you can toggle the door.

Then, hook up the lever or button to the two pairs of pistons.

The, flick or press the lever or button to see if it works. Notice how the door now stays open and closes when it's supposed to open.

(Refer to the picture above if you need help, but you don't have to use that same design as me.)

Step 3: Create a NOT Gate

Now, we need to create a NOT gate in order to fix the underlined problem in step 2.

A NOT gate basically outputs the opposite of the input. Let me explain.

As seen in the picture above, the piece of dust left of the orange wool (the NOT gate) is off. That piece of redstone is connected to the lever which means that the lever is off. When I flick the lever I want the door to open, but since it has no power BEFORE I flick the lever I end up closing it instead. How do we fix this? NOT GATE!!!

The NOT gate looks at the redstone coming from the lever and notices that it's off. The NOT gate knows that when the lever is turned off, he has to turn on & when the lever is turned on, he has to turn off.

Step 4: Add Final Touches & Details

Now all you have to do is make it pretty! You can click on the video to see what mine looked like once I was finished.

NOTE: If you watch the video then you'll notice how I added a second button that allows you to get out, but left out in the tutorial. If you'd like me to add how to create that then let me know! Thanks.

Have any questions? Let me know!