Gather materials: sticky pistons, redstone dust, redstone torches, building blocks, levers or buttons, and any decorative blocks for the door
Choose a flat wall area with enough space for the door opening and redstone wiring
Make a 2-block-tall by 2-block-wide doorway, or any size you want for the door
Place sticky pistons on both sides of the doorway facing inward toward the blocks that will move
Place the door blocks in front of the pistons so they can be pushed and pulled
Connect the pistons with redstone dust so they activate together
Add a lever, button, or pressure plate as the input source
Run redstone from the input source to the piston circuit
Test the mechanism to make sure the pistons extend and retract correctly
Adjust the redstone layout if any pistons do not activate at the same time
Hide the redstone wiring behind walls or under the floor if desired
Repeat the same setup for larger piston doors, using more pistons and a wider doorway
Use repeaters if the redstone signal needs to travel farther
Use observers, slime blocks, or honey blocks for advanced piston door designs
Cover the mechanism with your chosen building blocks to finish the door design