Raspberry Pi is a small, low powered motherboard contains 512 RAM, combined CPU and GPU. It has LAN, 2 USB, HDMI input, Audio Out, SD Card reader and S-Video connectors.
We can have many Linux distribution OS on it. To configure, we just need to attach SD Card to it. SD Card could range from class 4 to class 10. In some cases Raspberry Pi could support less then class 4 cards too. It could be powered through mini USB mobile charger.
Let's get started with installing OS on SD Card. There are various ways to install OS. Like we can download OSes through http://www.raspberrypi.org/downloads and follow the instructions given on it. There is something BerryBoot multi-boot loader through which we can have more then one OS on Raspberry Pi and boot OS according to our need. http://www.berryterminal.com/doku.php/berryboot instructions could be followed to install OS with very simple steps. You need to have internet connection on Raspberry Pi to install OS. It could be done by connecting through LAN or some Raspberry PI WiFi dongle.
Give it a try to Raspbian wheezy and XBMC OS. Raspbian wheezy is similar to any other Linux distribution OS. Through XBMC we can convert normal TV into smart TV or can have HTPC. It is able to play Full HD video and also it could be controlled through mobiles, slates or some TV remotes. XMBC is having tons of features through it's various add-ons.