So far we have shown you how to use Unity and be productive creating a scene, but with pretty simple content. Inherently, Unity is not a 3D modeling or asset creation tool. Rather (as the name Unity suggests), it's a unified platform for pulling together content from a variety of sources to assemble and program a game or experience involving animation, physics, rendering effects, and so on. If you are a 3D artist you may know how to create content in other programs like Blender, 3D Studio Max, or Maya. If not, you can find a plethora of models on the web.
One terrific source is the Unity Asset Store (https://www.assetstore.unity3d.com/en/). Many asset packs are free, especially starter ones, with possible paid upgrades if you want more. If you are looking for a few things to get your learning and experimental projects going, here are some of my free...