Welcome to..
For starters, what is Minecraft?
Minecraft is a Java game which is made by an Indie developer( called Notch ).
It consists of game objects aka blocks(everything is made out of them).
Now guess what the game is all about. First thing that pops into the mind is Mining is it not?
Actually mining is one of the many things you do in the game but yes, it is mainly bout mining.
You can chop wood, craft, make traps, blow stuff up, fight with mobs, make coasters, make cannons, build huge fortresses and last in this list(there are more things to do) is riding mobs(Pigs ^^)
There are a few versions of the game.
Creative: A gamemode which is free, with every block available, no crafting, no mobs, limited worlds.
Indev: The gamemode which came after Creative, and costs 10 dollars, it has got mobs, caves, crafting and limited worlds.
Infdev(Alpha): It also costs 10 dollars but, you only have to pay 10 dollars once to get both indev and Infdev. Unlimited, randomly generated worlds, different mobs, actively being developed( Every other friday theres a secret update), redstone(gmod wire, but very very basic aka theres a switch the redstone and a door, hit the switch and the door opens, easy as cake, but you can make timers, clocks, calculators with it, go look at the wiki to know more.)
Infdev(SMP): The currently very very bugged survival multi player, no mobs, broken stuff..
Links:
www.minecraft.net Minepedia:
http://minecraftwiki.net/wiki/Main_Page Redstone circuits:http://minecraftwiki.net/wiki/Redstone_circuit
Cannons:http://www.minecraftforum.net/viewtopic.php?f=35&t=19701
Traps:http://www.minecraftforum.net/viewtopic.php?f=35&t=31249
Official Guide:http://www.minecraftforum.net/viewtopic.php?f=35&t=17021
The largest project ever:
http://www.minecraftforum.net/viewtopic.php?f=35&t=18278