You'll have to set them up as animations to show when you actually present the slides.
To set these up, create the four objects you'd like to reveal incrementally.
- Right-click on the first object you want to reveal and select Animate
- The animation right navigation menu will appear, allowing you to select how you want the object to appear (fade in, etc) as well as the timing of the reveal (slow, fast). You can also define what action will cause the object to animate (defaults to on-click)
- Repeat process for the remaining 3 objects
You'll see the final product of all the animations in the right-menu. Once you create all the animations you want, you can reorder, change, or remove the existing animations, as well as add new ones.
Here's a screenshot (below) as well as a link to the help article on creating animations.