so they aren't selling it

Yes they are, they are offering the information they have about their users to their advertisers. If its bad or good is a debate for another time. But the fact is you are the product, your information is the product they are selling.

What kind of information do they offer to advertisers?

Citation from Google: "We try to show you useful ads by using data collected from your devices, including your searches and location, websites and apps you have used, videos and ads you have seen, and personal information you have given us, such as your age range, gender, and topics of interest."