You will find the parallax controls on the 'Layout' tab, which is visible after selecting an element. The default setting for parallax is 'off'. You can turn it on by selecting the checkbox, and then all the parallax control settings will appear:
What is a parallax scroll?
Important: The element you should select as 'parallax' element is the foreground element. The controls in the panel will define how this foreground element moves compared to the background element during scrolling.

Foreground element = the selected element
Background element = the selected element's container or parent

The background element should typically have a higher height than the visible screen to create a nice visible parallax scrolling effect.
Once you’ve set those options on your element in the box container, try scrolling up and down in the editor. To increase the time the parallax scroll should affect the element, increase the height of the box that contains it. You can change the start and end scroll effects too to further tune when your elements’ parallax scroll settings trigger and end. Different elements in the same box container can have their own unique parallax scroll option. This makes the parallax scroll effect even more apparent when you can compare scroll rate differences between two elements on-screen.
It is a design effect where the background content moves at a different speed than the foreground content while scrolling.

Creating a parallax (scroll) effect is not hard, as long as you plan out how these two elements (background and foreground) will interact with one another.
The example above is an illustration of this principle. As you scroll down the page, the background box scrolls at the regular speed of the page scroll, but the (foreground) text box scrolls at a lower speed. Because it scrolls slower, it appears to move from the top of the background box to the bottom of the background box during the scroll.
This text element is on the foreground, with parallax scrolling enabled. Desktop only!
Parallax Scrolling
Parallax scrolling is only available on desktop