I have got my Raspberry Pi up and running using a Sandisk Class 2 2GB SD card I had lying around using the excellent instructions here http://elinux.org/RPi_Easy_SD_Card_Setup.
In the list of Working SD cards here http://elinux.org/RPi_VerifiedPeripherals some people are using upto 32GB, Class 10 SD cards.
Could someone explain...
What does the SD card do?
What is the advantage of one SD card Class/Size over another for the Pi?
Does it work like the C:drive on your computer? can you store stuff on it?
I am a complete novice.