These are objects that do something when they receive a redstone signal.
Doors and Gates
All doors and gates can be opened and closed using redstone. Iron doors can only be opened with redstone; wooden doors, fence gates and trapdoors can all be opened either by hand or with redstone.
Why would you use an iron door? Wooden doors can be broken down by zombies if the game difficulty is set to hard, and villagers can open and close doors.
Redstone lamps are made from redstone and glowstone, so you'll have to brave the Nether before you can make them. They light up when switched on by redstonepower.
Pistons are blocks that extend when activated by redstone power, giving the block next to them a push.
Normal pistons push a block, which then stays in its new position when the piston retracts. Addition of a slime ball creates a sticky piston, which pulls the block back when the piston retracts.
TNT is made from sand and gunpowder: it goes BANG when activated by redstone power. It can also be set off by hitting it with a flint and steel, or by contact with fire.
TNT has a 4 second fuse, so you have time to get away if you set some off by accident.
Droppers and Dispensers
Droppers and dispensers are similar-looking containers, that can hold nine stacks of items, and release them one at a time when they receive a redstone signal.
Droppers eject items gently, or feed them into an adjacent container such as a chest or hopper. If an item is dropped on the floor, it will be as if the player had dropped them, and they will disappear after 5 minutes.
Dispenser also eject items when triggered, but for many types of item they don't just spit them out, they operate them as if the player had performed a right click.
Projectiles (arrows, eggs, snowballs, splash potions, fireworks etc.) will be fired rather than dropped.
A dispenser armed with a flint and steel will set fire to anything flammable in the block in front of it.
If TNT is dispensed, it will be placed and ignited, and unless the dispenser is hanging over the edge of a pretty high drop, it will be destroyed.
If bonemeal is dispensed, it will fertilise any crops directly in front of the dispenser.
A dispenser containing a bucket of water or lava will place the water or or lava in front of it when triggered and if triggered again it will suck the water or lava back up.
A dispenser will place minecarts on rails or or boats on water, ready for the player to get in. If there is no rail or water in the right place, it will drop the item rather than placing it.
Hoppers are devices that can collect items from the environment and transfer them to other containers. A redstone signal will swith a hopper OFF, and stop it from transferring items.
These play musical notes, depending on their tuning (right click to tune) and the substance on which they are placed.
Three kinds of minecart rails respond to redstone signals.
When rails are placed to form a junction, one of the rails will curve to connect, two of the tracks. A redstone signal will cause the curved rail to switch orientation, allowing tansportation in a different direction.
These rails push minecarts along the track when switched on, otherwise they act as brakes.
These rails, when they are switched on, will activate certain types of minecart. They will cause a TNT minecart to explode, or they will stop a minecart with a hopper from…hoppering.
Repeaters and Comparators
These blocks are powered by redstone, but they have their own page.