Yeah its the most wonderful time of the year for me; sitting at my desk, contravening my company's IT fair use policy by streaming the commentary, changing the TV from Sky News to Channel 9 during my lunch breaks...awesome. (I'm Australian, if you can't tell)
*puts on top hat, lights corn cob pipe, lights fire, calls his cocker spaniel over, pours some scotch, sits in rocking chair*
Well, you see young lad, test cricket was "cricket" until the 1970s, when a media tycoon created this fandangled contraption known as "World Series Cricket". This restricted the game to 50 overs per side, meaning a game could be completed in a day (hence its name, one day cricket). By comparison, a test match can go for up to five days, with up to 90 overs play each day and a team being able to bat as long as they can; although teams normally will bat for about a day. There are also two innings per team in a test match, so a team bats then bowls then bats and then bowls (although this can change based on match circumstances).
One day cricket basically guarantees a result, whereas a test match can go the full five days and end in a draw. I won't get into the intricacies of this...it will probably blow your mind. A more recent phenom is 20/20 cricket, which as its name implies is limited to 20 overs per side. There are a number of other rule changes that give rise to much more aggressive batting and high scores, in my mind to the detriment of the form of the game. T20s are particularly popular in India.