I don't have a lot of info on it, but since no one has replied for awhile, I will try to help with what little I know.
To oversimplify- it takes a lot of money to make a lot of money, and it's more of a gamble than the regular way of playing with the stock market.
The idea, to oversimplify- buy a bunch of shares in the morning, see if they go up, then sell them before the market closes.
Say you buy 1000 shares of Company X at $20/share. At the end of the day, the stock went up .10.
$20 X 1000 shares= $20,000 to buy.
.10 x 1000 shares= $100 profit
So as you can see, to make a good profit you need at least one of two things
1) A LARGE amount of cash to buy enough shares
2) A LARGE enough increase in stock price at the end of the day
If there isn't an increase in the price, and you are after the "quick buck" (which is kind of what day trading is about) you will still need to sell your shares b/c you do not know what tomorrow will bring and could lose even more money.
My brother's greatest one day profit was $30,000. I don't know what his greatest one day loss is though