First Step, Go to your HTML editing website and open the website you wish to add the video to.
Now with that open. Go to your video viewing website of choice. In this case I will be using YouTube. Go to your homepage which will something like this:
Then click the search bar (pictured below).
Once you're here type in the name of the video you want to upload.
Click on the video as you would if you wanted to play it.
Then click on the button that says "Share"
An embed button will appear, click on that button.
Once clicked, a code will appear along with a preview of the video
When here click the copy button and go back to the HTML page you opened early
In the HTML side your website. Paste the code you copied, click the save button, and you're done! (Click the view button to see your work)