How do I implement a comment section into my rails app?

So I followed a tutorial on Youtube so that I could make a simple video sharing website such as Youtube itself -> https://www.youtube.com/watch?v=uV1hWKtza0g
I want to inplement a comment section so that the user can input comments. I saw several videos on how to do this but it was all for blogs and not a video sharing website. It would be greatly appreciated if you check out the video to get a sense of what I'm doing better. THANKS!