Every wonder why advertisements on Facebook and YouTube are SO relevant? Or why a website will pop up as an advertisement elsewhere after you've visited the website? Because your cookies are on! Disable your cookies. The internet is watching you. Your computer saves cookies, and every website you click on, the website gains access to those cookies, AKA HISTORY of websites you've been on. That way those websites can pinpoint your interest through what you've clicked on.
Also...metadata. Metadata is the information on what you share. Every single picture you take-- with your phone, laptop, camera, whatever, has metadata. No good. Metadata is information from how you've taken a picture, date, time, and location. Every time your share a picture, a website receives this information to find out about you. And in turn, this website will share advertisements with you about a number of things. It will share ads based on you location, your age (if you're still logged into Facebook), time, as well as based on your history, from cookies.
For you Facebook users, peep this: https://www.facebook.com/about/privacy/your-info
(Side note/TL;DR: If you were wondering why advertisements are becoming WAY too relevant nowadays... well here's why. Protect yourself from getting your information stolen. Google Chrome may be okay, but try switching to Firefox, and turning off your cookies and history. If a website asks you to turn your cookies off, that website is doing something is shouldn't be...)