If you are trying to embed a video form youtube into your website, the easiest way to do it would be to right click on the video and select the ‘Copy embed code’ option, then just paste the copied code into where you want the video element to be in the html code. Below is an example of what a copied embed code looks like.
<iframe width="853" height="480" src="https://www.youtube.com/embed/PmmQjLqJQlY" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
After you paste the copied snippet into your html code, you can play around with the parameters like width and height to see which values suit the best on your webpage.
Hope this helps you.