Google AdSense work in earning from YouTube:

• YouTubers join with two objectives in mind: 1,000 subscribers and 4,000 hours of channel Watch Time. After that, creators can apply to join the YouTube Partner Program (YPP) and monetize their work.
• To collect ad money, authors must set up a Google AdSense account as part of the YPP application.
• On creators' videos, Google AdSense places advertisements. Google AdSense employs personalised targeting to match relevant advertising with viewers' interests, increasing the likelihood of such ads being seen.
• YouTube creators get compensated for their efforts.
• Because Google AdSense and the YouTube trip are both complicated, there are a lot of fine print things to be aware of. The most crucial part is the method for calculating revenue. You won't get all of the money from commercials if you join the YPP; creators get 55 percent of the revenue, while YouTube gets the other 45 percent. 

Read More: How does YouTube AdSense work?