When a company goes public who profits from the sales of shares the corporation or the stock holder?

[Nicigil]

When a company wants to go public don't the shareholders have to sell off some of their shares in order for there to be stocks to buy? So in this case when someone buys the shares the money should go to the stockholder but I thought the point of going public was to raise money for the CORPORATION to be able to grow! Hope you get what I'm saying! Also when a company goes public do the shares increase in value? For example before the initial I.P.O of Facebook people were saying Mark Zuckerburg would become even more wealthy than he was making him worth billions more than he was worth before but if he's selling shares how can he and the corporation itself make money??? Any help is appreciated!