Purpose: Sometimes it is not possible to model all the necessary components for your project. Instead, there are many freely available asset resources that can be used under certain license conditions.
Description:This post serves as a reference guide for importing external 3D models and other assets (textures, materials, sounds) from online resources.

Materials: Computer, Unity 2019

Instructions:

This Link includes several good resources for finding freely available game art online. Specifically you should look for file types ".fbx" and ".obj" these files are fully supported by Unity. Other file types may work with a bit of tinkering so don't discount an asset if you think it would be useful for your project.