Well,let's say it's a beautifull sandbox game using many elements to create a massive amount of things to do! You can,
.Kill things
.Make houses
.Mine!
.Create castles
Any many more!
Since there is absolutely no storyline in Minecraft,all you need to do is spawn,chop down some trees and make a house.Simple!

Minecraft is $21.99 USD,and can be purchased at minecraft.net.There is a great video for Minecraft that shows the graphics and capabilities of the game's enviorment creating engine.Now then,if you need help getting started in the game,need to learn crafting recipies or how to find/use items,go to minecraftwiki.net,the best Minecraft Wiki you can find!

If you have any questions,visit the link I just told you about ._.

Here's a tip:look out for tall moving green things with a black face,those kill you :3