How to do simple animations where object shows from left to right?

I'm trying to create the animations below where the object is shown from right to Left, and where the object slides and shows.

They seem to be very simple and essential animations, but I can't find any functions that do this automatically. I end up placing a giant square with the same background color and sliding it to create this animation.

Can someone guide me on how to do this in a more effective way.