Setting size of embedded video on pages & posts

First, LOVE the customizr theme, I have been SO happy with the look and flexibility for my web site at https://www.gooseling.com!

My question is how to properly set the size of videos I embed on pages and posts. I tested embedding my first Youtube video which was super easy (just putting the Youtube URL on a separate line without the live link and no other text). The only catch is the width and length of the embedded video that appears on the web page or post is huge. I haven’t made it live yet because it looked funny being so big.

I read the tip to add this code to the theme’s functions.php file [if ( ! isset( $content_width ) ) $content_width = 600;] but that the number will vary specifically for the theme. Is that right? Is this how to do it? The source of where I read this tip was https://www.wpbeginner.com/wp-themes/how-to-set-oembed-max-width-in-wordpress-3-5-with-content_width/ but I’m not a programmer so wanted to check to see if one of you have advice for how to do this properly. I want the size to look similar in size to what you typically see when you go to a random youtube page (here’s my test youtube video, we plan to upgrade it to a better quality one soon).

Thanks so much for your help!