I don't understand how the actual buying and selling works. I'm sure someone does.

Let's say I sell 100 shares of XYZ. I know about what it will fetch. However, I don't understand exactly who buys it and at exactly what price.

Is there someone who wants exactly 100 shares of XYZ? Does someone else want 1000 shares, and mine is a part of the deal? Who buys my shares and puts it together? Exactly how does the price fluctuate? Is someone there offering $0.50 less than what I'm asking? But I'm not really asking a set price, am I? If no one is purchasing XYZ at the moment do I have to wait a few hours? Why hasn't that ever happened?

I'm not talking grand theory, I'm wondering about the actual mechanics of the matter, who buys the shares the second my broker forwards the offer to sell and how that person sets a price.

Thanks for whatever attention this is given.

Arf