I have to ask this but...
What exactly is Minecraft? Everyone keeps talking about it and playing it, but I never understood the concept of it...
Something what Scotty said...But I'll add in a bit more detail. (WTH Scotty, are you putting Minecraft in my iM@S?)
Minecraft is a world 8x the size of your regular earth (According to what my brother said). What are you supposed to do in there is to
mine various objects to
create or build things.
Such as:

If you're playing survival single player mode, then monsters will pop out during nighttime. Like zombies, skeletons (that shoots arrows), creepers (green armless suicide bombers) and spiders.
During daytime you got some harmless monsters like: cows, chickens and pigs.
Oh and one more thing if I remember about 20 minutes = 1 day in Minecraft.