Retroactive gitignore

Lets say you have a local repo full of garbage items and some very personal details and now you want to publish it for the world to see.
How do you stop all tracking of thouse files and delete them from the git history?

Well it simpler than it seems

git rm -rf --cached .  

And then

git add .  

I do not know how these commands work but they do so ¯_(ツ)_/¯