To start off you need these items [2x1]:
1 Lever
4 of any block (Non-Transparent)
1 Redstone Torch
2 Sticky Pistons

Method [2x1]:
1. Clear some space
2. Place 1 (Non-transparent) Block down
3. Put a lever on the Block
4. Put a redstone torch on the block opposite to the lever.
5. Place 1 (Non-transparent) Block above the Redstone Torch.
6. Place 1 Sticky Piston next to the Redstone Torch and 1 next to the block on step 5. (Use your commen
sense to find where you put it)
7. Your done, it should look like this (Lever is opposite to redstone torch):
8. To make it 3x1 you need to put 1 redstone on the block above the redstone torch and put a piston beside it.