In this inscrutable I will show you the basics of redstone and show you how to use it. Redstone is useful for survival (bases, minecart stations, TNT cannons ect.) As long as you know the basics of redstone you can build lots of cool things.
Step 1: Inputs and Outputs
Inputs trigger outputs. For example when you click a button that is next to a door it opens. This is the base of all redstone contraptions. There are many things you can use as inputs (levers, buttons, pressure plates, ect.). There are also many things you can use as outputs (pistons, doors, gates ect.)
Step 2: Putting Inputs and Outputs together (Wiring)
For somethings the inputs and outputs can directly interact, but other times they can't. for these situations we use redstone wiring.
In the picture one you can see a lever connected to some redstone wiring. When you activate the lever the redstone is activated which powers the door. in picture two you can see a lever hooked up to Redstone wiring which goes to two pistons. When you activate the lever the redstone current flows directly into the top piston activating it, but it also powers the block it runs into which is why the bottom piston activates. This is very use full and it is why picture 3 works.
Step 3: More about wiring
wiring does have its limits how ever. Redstone wiring can only run 15 blocks with out dying. How do we get around this? We solve it with repeaters. Repeaters do 2 things the repeat the signal so it will run another 15 blocks and it provides a delay the father apart the two switch like pieces on the repeater are the longer the delay. We call these delays ticks.