It is used mainly by Architects but can also be used Furniture Designers, Set Designers, Product Designers Furniture Designers and Engineers, in fact, anyone who wants to create a visual or "mock up" a 3D object or space of any kind be it virtual or physically built.

The "Make" version of Sketchup is completely free to download and use, and if you want some more specific features such as exporting simple animations you can pay for the full version which is called "Pro". For most people though the functionality of "Make" is generally enough.

More info - https://skl.sh/2LWiRti