The creeper was a coding mistake
The CREEPER exists because of a typing error. Markus Persson, building the game largely on his own, was trying to model a pig and entered the dimensions in the wrong order, producing a tall, thin, upright creature instead of a long, low one. He liked the look of it, gave it a mottled green texture, and decided it should sneak up behind people and explode.
The whole project had that quality early on. The first playable version was written in about a week in 2009 and put online for strangers to try while it was still being made — unusual then, completely normal now.
Every world is really one number
A Minecraft world does not exist until you walk into it. The landscape is calculated as you go, from a single starting number called the seed, so the same seed always produces the same world: the same BIOME in the same place, the same village, the same cave under the same hill. Players share good seeds like fishing spots.
That is how the worlds get so absurd. One is around 60 million BLOCKS across — something like seven or eight times the surface area of the Earth — and nobody has explored more than a sliver of one. There is nothing at the edge either, except the point where the game politely declines to generate any more.
A computer hiding inside a toy
REDSTONE behaves like electrical wiring. It carries a signal, and its components let you switch, delay, invert and combine those signals — which happens to be exactly what digital logic is made of.
So players build machines with it: automatic doors, traps, farms, calculators, clocks and working memory. Some have gone considerably further and constructed functioning computers inside the game, one of which was made to run a crude version of Minecraft itself. It runs at a fraction of a frame per second and serves no purpose whatsoever, which is rather the point.
Nobody tells you what to do
The game ships with no instructions, no story and no goal. You arrive at SPAWN with empty hands and have to work out that punching a tree yields wood, that wood makes a CRAFTING table, that the table makes a PICKAXE, and that the pickaxe makes MINING possible. Then night falls, a ZOMBIE and a SKELETON turn up, and the argument for a shelter and a TORCH makes itself.
This is why it ended up in schools. There is an education edition used for geometry, chemistry and programming, but the real lesson is the one the game teaches by refusing to explain itself: try something, watch what happens, remember what worked.
The best-selling game there has ever been
Over 300 million copies have been sold, making Minecraft the best-selling video game in history by a wide margin — achieved by a game that looks as though it was drawn in 1995. Microsoft bought it in 2014 for around two and a half billion dollars.
The blocky look was never a limitation. Every cube can be removed and replaced by anybody, which is simple enough for a five-year-old and open enough that people have spent years building cathedrals, working cities and scale models of their own schools, one COBBLESTONE at a time.