Google AdSense
https://www.vlognation.com/make-money-youtube-google-adsense/
“YouTubers” get paid by the number of advertisement views they get on the video. This is often substantially lower than the total views the video actually receives. However, not all videos posted on YouTube are eligible for payments. To become eligible, the user has to follow a few steps with one of them as connecting your account to AdSense. AdSense is a service provided by Google, which tracks your activity on the internet and uses this information to post relevant advertisements on your YouTube channel.
AdSense can collect all of this information by recording your clicks on the internet or by collecting keywords. They see what web pages you visited, what you shopped for on Amazon, etc. All this information gets stored in a network for your profile. From here they will use the websites most visited by you and match these with keywords. Now that the information is organized, AdSense makes a decision on what type of advertisement to post on a video. YouTube is one of the largest web pages on the internet so most advertisers will choose to post ads on this page. AdSense increases the valuation to the advertisers because they match the ad with the appropriate target audience. This benefits both ends of the party.