google makes money by advertising. people or companies who want people to buy their product, service, or ideas give google money, and google shows an advertisement to people google thinks will click on the advertisement. google only gets money when people click on the link, so it tries to know as much about people as possible to only show the advertisement to the "right people". it does this with google analytics, which sends data back to google whenever someone visits a website. from this and other data, google makes a profile about the person and then uses this profile to figure out which advertisements to show.