How to create a many to many relationship using mongoose [closed]

I’m following a tutorial on the official MongoDB Developer docs (https://www.mongodb.com/developer/languages/javascript/getting-started-with-mongodb-and-mongoose/) and at the end it says that the blog post could use some comments so that would be a many to many relationship and would be a great practise and use case for many projects but it doesnt explain how to create that. Could someone explain and add the code of how to add comments to a certain blog.

I’ve roamed through many blogs and Youtube video’s but still haven’t found anything that gives me a clear example.