Thank you for your reply, jinkels.
I am a beginner and I make beginner mistakes. This is what I had done: I have a directory that contains my repositories. Somehow I couldn't upload to Github at the time and I decided to run the git init command to this very same folder.
When you then run git status, you get the above message. The folders are not added, but it didn't feel right to me.
So, how to run an un init command? The answer is simple: remove the .git file from the directory.
And everything is as it should be.