html additional information icon/button

So I want to add another feature to my website. It is about key figures. and some of them should be explained in more detail. I want to make it as a small information icon next to the word, which should be explained. When u hover over this information icon(or click), a small pop up should appear with all the needed information to understand the meaning of this key figure. Similar to the following picture pic here

I don't know how to search for such a tutorial or how to completely program it. Does anyone know a good video/blog/how to search for sth like this or has some code? Thank you very much, Best Regards, Julian