Minecraft it's an open world construction game. This game is about destroying and placing different kinds of blocks in order to build anything you want. The game is very often updated, there are weekly snapshots that includes new things, and when there are enough new things, a new official version is released. Minecraft is actually at 1.4.2 official release.
Items and blocks
Characters:
Steve: This is the principal character, you control him. It is not certain if he is really named Steve, but everyone calls him like that.
Zombie: This is a hostile mob. It appears at night or in dark places. If it touches you, you take damage. If you are in hard difficulty, it can break doors. It burns at day.
Skeleton: This is a hostile mob. It appears at night or in dark places. It has a bow, so he can shoot from a distance, causing you damage. It burns at day.
Spider: This is a hostile mob. It appears at night or in dark places. If it touches you, you take damage. If you see it at day, it won't attack you. There are also Cave Spiders, that only spawn in abandoned mineshafts, they also damage you if it touches you, but it also poisons you.
Creeper: This is a hostile mob. It appears at night or in dark places. Creepers follows you and when they are close enough to you, they explode. They are afraid of cats.
Enderman: This is a neutral mob, if you attack it or look it in the eyes, it will attack you. It can hold some kinds of block. It makes creepy sounds.
Cow: This is a pacific mob. If you kill it, it will drop raw beef and leather.
Chicken: This is a pacific mob. It can lay eggs. If you kill it, it will drop feathers and raw chicken.
Pig: This is a pacific mob. You can ride it with a saddle. If you kill it, it will drop raw porkchop.
Sheep: This is a pacific mob. You can shear it in order to get wool. If you kill it, it will drop wool.
Wolf: This is a neutral mob, if you attack it, it will attack you. You can tame it with bones and it will become a domestic dog.
Ocelot: This is a pacific mob. You can tame it with raw fish and it will become a domestic cat.
These are the most known characters in the game.
Game Modes:
Creative Mode: In this mode you are able to fly, destroy any block instantly, have access to an inventory in which you can get any item or block you want without having to mine it and you can't die. This mode is good for people that are new in Minecraft, to test things or just to build gigant things.
Survival Mode: In this mode you have to survive, you have a health bar that decreases when you take damage (fall damage, mob damage, explosion damage, etc), if this bar gets empty, you die. You have a hunger bar too, you have to keep it full by eating in order to restore your health, if this bar gets empty, you'll start to get starvation damage. You need to mine blocks or craft them in order to get them. At night, monsters spawn.
Hardcore Mode: This mode it's pretty much the same as survival, but it is always in hard difficulty and if you die, the world will be deleted.
Biomes:
Forest: These are biomes with a lot of trees and tall grass.
Plains: These are biomes with almost no trees, no hills and a lot of tall grass. You can find villages in this biome.
Desert: These are fully sand biome. It doesn't rain in desert biomes. You can find villages and temples in these biomes.
Swampland: These biomes has a lot of water, lakes, trees and vines. You can find witch huts in these biomes.
Jungle: These biomes has a lot of trees, including very tall ones, vines and it has very green grass. You can find temples in these biomes
Ice plains: It's pretty much the same as normal plains, but covered in snow.
Taiga: It's pretty much the same as forests, but covered in snow.
Extreme Hills: These biomes has a lot of mountains, including very big and tall ones. There a lot of cliffs, valleys, lakes, overhangs and peaks too.
Ocean: These are fully water biomes. These biomes are pretty large.
Mushroom Island: These biomes has mycelium instead of grass, and huge mushrooms instead of trees.
Conclusion:
We think this is a pretty funny game, you can do whatever you want, you can explore, go minning, explore the world, kill mobs, build things, etc. You can also set up a server so you can play with your friends. There are a lot of blocks and items so you'll never get bored, there are a lot of possibilities of things to build.