To first embed a video you must find a video. What I have done is I went to "youtube.com" and found a random video.
After I found my video I clicked on the video then I scrolled down till I saw the "Share" button. Click on the "Share" button.
Once you have clicked the "Share" button you should see this popup. Go ahead and click embed.
After you clicked embed you should see some code, you will want to copy this code.
Now that you have the code copied you can paste it inside your website. Just like this
Here is how the final product should look like once you're finished