As with all computers, your Raspberry Pi requires a boot-loader and a suitable Operating System to boot. Some Raspberry Pi's comes with pre-installed SD card, but if you didn't receive one you will need to prepare your own.
You can use the BerryBoot installer if your Pi is connected to the Internet.A small zip file containing the BerryBoot system files is required to be extracted to an empty SD card .Then boot up your Pi with the SD card inserted and follow the on-screen prompts to complete the installation. BerryBoot allows you to install more than one Operating System.
To prepare your SD card you have to download the SD image (the data you will write to the card) from a mirror or a torrent . It is recommended that you verify the image with the SHA-1 checksum provided in the download page. After successfully downloading the image extract the image file to a folder of your choice.Now insert the SD card and note the drive letter assigned.Format the SD card to avoid any troubles.You will need an utility (Win32ImageWriter) to make your SD card bootable. Locate the image file that you have extracted and select the drive letter in device box of Win32DiskImager .
Then you need to hit on 'Write' followed by ‘Yes’ when confirmation box appears . The burn process takes around 3 minutes and upon completion you will get a pop up ‘Write Successful’. Now remove the SD card from your computer put it in your Raspberry Pi .You can expand the partitions using configure script to use all of the SD card if you have used SD card of capacity greater than 4 G.B.