So look. If you want to make a secret door, you need to wire the redstone above a redstone repeater. Than wire it to a piston, and carve out a staircase to wire it up to the top block. Than, use a comparator to wire up the redstone at the bottom and connect the redstone to it. This is to delay it for long enough so you can go in. Than what you do, is power the redstone with a torch and than a detecter And power that to the door. Than put another detecter near the area, wire that with the redstone near the door. Than what you want to do, is make a stone slab and place it somewhere at the bottom of a hole, and power a hopper to go there. Than let it lead to the two droppers. Put a pressure plate near near the back there, and make sure the wires are connected. This should allow you to drop an item in, the door opens, and then the item gets sucked into the hopper, and the dropper gives you back the item inside of the house. And there you go. You got yourself an easy redstone door that opens when you drop an item into the hole.