Tip: If you have never used the Unity Editor before, start with the First time users documentation.
Everything in the Unity documentation, other than the 2D section, is relevant to 3D game development.
The first two choices you must make are your 3D render pipeline and the platforms you want to support. These choices affect each other: some platforms don’t support the High Definition Render Pipeline (HDRP).
To get started, review the documentation for:
If you need to import assets from third-party applications, check that all applications can produce formats that Unity can import. For more information, refer to Supported asset type reference.
What you focus on next depends on your role, but if you’re a sole creator, you might want to consider the following: