GitLab – How to Upload a File via Web Interface

I think this answer explains it best. Negation only works to re-include files that have been explicitly ignored by another rule. When you ignore an enclosing directory, Git doesn't even descend into it and hence never sees, nor explicitly excludes, your file.

The answer below the one above gives you the solution: You have to create one or more rules which build a set of paths that explicitly excludes everything you want to exclude including your file at which point you can negate the exclusuion for it or any of it's containing directories.

To add a file/folder, use git add command. Then use git commit to commit to your local repository. If you want to send it to the base (to be available to other users, for instance), you should git push your changes.

Remember to, before adding the files, to create a .gitignore file in order to avoid persisting binaries and auto-generated things (dlls, exe, etc) - these shouldn't be on repository.

Maybe you should search for some tutorials, documentations. Maybe this would help you improve your knowledge on git.