"Most of the free apps you'll find on the Play Store have ads. These ads are personalized — in other words, they're for products and services Google believes you might be interested in. The way Google knows about your interests is by collecting data from your smartphone, including your location and app usage. While personalized ads have their advantages, the collection of data is unsettling.Google is able to collect this data using what is known as an advertising ID. This is a unique identifier attached to a packet of data that contains bits of your browsing habits and history, though it is anonymous in theory.Google then sells ad space to companies by promising they'll match the ads users see with their personal interests using the information contained in their advertising IDs. For privacy-conscious users, Google has provided a way to stop this form of tracking with a pair of settings built into Android."
And here's how to opt out of a few things on google itself, make sure you are logged in with the same account used on your phone when you do it (that's if you do the adjustments on your PC, if you do them on your phone it should already be logged in with that account).
