OK here's my take on it. Oh and SPOILER if for some reason you haven't seen this movie (which is an Eddie Murphy/Dan Aykroyd classic)
The two brother's get their fake early crop report which says that the years orange will be bad making oranges scarce and their price sky rocket. They start buying up all the shares expecting the decrease in supply to jack up prices so they'll make a killing. Other traders seeing these big players trying to corner the market hop on the band wagon and help drive the pre-crop report price even higher. Now Eddie and Dan wait until they feel the price is high enough and then start shorting the stock (selling shares they don't have at an inflated price expecting the price to drop, called short selling http://en.wikipedia.org/wiki/Short_selling
) Then when the report is released and it's made known the the crop was actually good instead of terrible increasing supply to meet demand and lowering the price since oranges wont be scarce, the stock drops drastically because everybody wants to sell and they fill all the orders they short sold.
So basically they sold a whole lot of stock at say $150 a share (they didn't own any stock at this point)then the stock fell drastically and they bought enough stock to fill what they sold at $80 a share giving them a net profit of $70 per share they shorted. I think in the movie it was probably much more drastic and they made a whole crap load of money.
The brothers (along with the rest of the traders) did the opposite, they bought the stock all the way on the uptake expecting the stock to go even higher after the report only to have the stock drop and waste a bunch of money, so they bought at $150 and then sold at $80 losing $70 per share, and ruining them.
No I may not be 100% right I'm an IT guy not a finance guy but if working at a finance institution for 4 years has taught me anything I think I'm close