Okay, let's go over the basics of Redstone circuitry. Once you start building with Redstone, Minecraft can become a completely new game. It allows you to craft essentially circuitry within the game and you can make intricate machines and really simple computers even. The things you'll be needing are some Redstone torches, which is like a regular torch, but instead of coal you use Redstone on top. You'll need a lever. Just one cobblestone and one stick on top. You'll need some Redstone repeaters. Three stone on the bottom, two torches on the side here, and one Redstone in the middle. You can also use other elements besides levers as your input. That's a stone button or a stone pressure plate. Those will also activate Redstone.
So let's head over here. I've got a lever set up as my input. It has an on and off state. For my output, I'm going to use a door. Now I need to use Redstone to connect my input to my output. Now that they're connected, when my lever is on my door is on, when it's off my door is off. Over here I've set up a simple inverter by placing a Redstone torch one block up and connecting that Redstone torch to the door. I've set the door to default to its on state. When I press my lever I turn off that torch. Now an off state for my input is an on state for my output. And vice-versa, an on state for my input is an off state for my output.
I can use this to make what is essentially a lock. If I think of this lever here as my input, turning it on and off does not affect my output. That's because this lever, my lock, is in the off state. I turn it on and now my switch works perfectly. That's because essentially both of these Redstone torches need to be off to effect the door. If either one of them is on, it inverts the flow and closes the door.
Redstone current can only travel 15 blocks. So if I turn that on, my door stays closed because you can see it getting dimmer and dimmer and dimmer to the 15th block here and it won't go any further. That's what Redstone repeaters are for. I place that on the 15th block and it will repeat that current another 15 blocks. Repeaters can also be used as delays. And they have four states of being. If I right click on them those Redstone torches get closer together, meaning there will be less of a delay as the Redstone current passes through them. So if I set all these to the shortest distance, that delay becomes much shorter.
These Redstone repeaters have four states of being. Redstone repeaters can also be used as one way gates. If I break this Redstone repeater and place it backwards, you'll see the arrow is now facing in the opposite direction. So current coming form this direction won't effect the output but coming from the opposite direction, it would.
I can also use repeaters to set up a simple clock. So the current from this torch is being delayed in this repeater and essentially turning itself on and off again in one continuous loop. I can use this clock to effect an ouput block over and over and over. So I'll build a path out here and place a note block. And you can tell I've already laid down a beat. I can right click on this repeater to change the amount of delay and speed that beat up. Let's continue the current in this direction, set up a repeater, wrong direction, set up a repeater that way. Some more Redstone and one more note block. So now because I have two repeaters, I can control each distance individually and have more control over the tempo of my song.
Okay that's enough of that. You can combine all these elements in different ways to make really intricate machines in Minecraft. So be creative and have fun.