How to add popup (window info) to Google Maps markers?

Question

JavaScript

I have a map with markers, I need to add popup text to these markers, like this https://developers.google.com/maps/documentation/j... .
No matter how I tried, it doesn't work. I beg you to help with this issue or show an example how to do it.
Here is an example of my map: https://codepen.io/alexander-rodionov/pen/MqpXyb

Answer 1

https://jsfiddle.net/6eLg3a8v/1/