Reveal object "underneath" page flow while scrolling

Hey people!

Can someone point me to a tutorial or explain me how to achieve an effect similar to the title sections on this page? http://history-of-animation.webflow.io/

In the example above, the numbered title sections’ background images are fixed, unmoved while its content scrolls up and down with the rest of the site’s content. This happens in every title section throughout the page.

How can I achieve this effect? Can someone point me to a tutorial or explain me how to do it?

Thanks!

Just add a background image and set it to fixed. Really easy!