How to add a local folder with a React project as a submodule to a repository?

Question

git

I have a project "React-backend" it was created by the expressJS library.
In this folder I created a new React application, Through the Create-react-app utility;
Now when I upload to gitHub all the change of the "react-backend" folder everything is uploaded there, except for my "React" project, it is tagged as a regular file, not as a nested project

, what's the problem?, how do I upload two projects to the repository at once, so that I can navigate through folders, etc.?