you use the internet, what you search for, the sites you visit, that's your personal data that they siphon.
browser with this ID was searching for this and that, and visiting these kinds of websites, send ads for things that match up with habits in that browser.
your name and personal details aren't relevant, they don't care about paltry things like identity, they care about behaviour, so they can send predictive information back to try and get you to buy things, and charge money to the people who want to sell those things to get those ads in front of you.