Minecraft is a very building based game developed by Swedish company Mojang, with hundreds of thousands of players from whole world. In this game you basically build whatever you want. Many people compare Minecraft with Lego sets, because this game is based at blocks. When you see Minecraft for the first time game graphic can be repellent, but after a while when you figure out basic things, then this game will provide a lot of fun to you.
There is two main game modes – survival and creative. You must go through survival mode because there you will learn how game really works. In survival mode you start barehand, without tools and weapons and you must made all that with resources which you will find in game. You must combine resources, in game that's call "crafting". With crafting you will make new elements, for example wood and stone can be axe or pick, wood and coal can be a torch etc. You must find recipes, because crafting in Minecraft is very important.
There is also some different creatures which will try to kill you, because of that you need weapons. And those creatures can kill you over night, so you need to find place for your home, of course with a lot of light. Or you can make a bed and sleep over night.
Also in game you will see creative mode. Here you will get all resources at one place, you don't need to make anything, just pick up whatever you want from your inventory and start building. This mode is great because here you need only a great imagination, you really can build whatever you want. Also this mode is common at online servers, you can play Minecraft online with many players, alone or in teams.
If you start with Minecraft online then you will need Minecraft account, you can buy one from official website. With account you can login at some server and see what other people do. Then you can ask moderators for permission to have your own place or you just can join some team and made with them large structures.
In Minecraft large structures mean really large, some teams spend a months on some buildings. But on every servers you must follow server rules or you can be banned very fast. Minecraft is game with "old school" design and maybe at first sight will be boring to you but believe me after a while you will play this game every day. So grab one account and enter in world of Minecraft right now!