Here's How To Figure Out Everything Google Knows About You
The more Google knows about you, the more it can match you to an advertiser who thinks you are an ideal customer. Advertisers are willing to pay more for ads served to ideal potential customers. For instance, airlines want to target people who love to travel. Children's clothing makers want to target parents.
Google uses a lot of methods to learn about you. There's the stuff you tell Google outright when you sign up for its services, like Gmail and Google Maps, or via an Android phone, like your name, phone number, location, and so on. Google also deduces information about you from watching your internet searches (what do you search for? click on?) and from the stuff you do with Google's products.
By visiting a site called "Ads Settings" you can see what Google knows about you.
It's not that easy to find Ads Settings. First, click on the link below or type it into your browser: https://www.google.com/settings/
Then click on "Account history".
Scroll down to Ads and click on "Edit settings".
This page shows you what Google thinks it knows about you including your age bracket, the languages you speak and ...
... including your interests.
From that page, you can edit that information or "opt out" of allowing Google to share your information with advertisers.