'Variance' is the technical term that we use in poker to describe the natural ups and downs of the game. The reason why you need to have such a big bankroll is because of variance.
So for example, if you play at the lowest limit online, which is typically 1c/2c with a $2 buyin, then you should have around $60 in your account before you play this game. I recommend having at least 30 buyins for any limit that you choose to play these days. This is the total amount of money that you have available to play poker with.
The next thing that you need is the correct poker bankroll. Poker Cheat Sheet - Have the Right Poker Bankroll
