Click the Share button under the YouTube video you would like to embed.
Click the Copy button next to the link provided to copy it to your clipboard.
In Canvas, navigate to the page you would like to add the video to, then click "Edit" at the top right of the page.
You should now have access to the Rich Content Editor. For more information on page editing in Canvas, see How do I edit a page in a course?
Move the blinking cursor to where you would like to insert the video in the Rich Content Editor.
Click the "Link to URL" button.
Paste your YouTube link into the text-box that opens and click "Insert Link."
You should now see the embed placeholder; when the page is saved, this will display the video on the page.
Save your page in Canvas. If your page is not yet published (and therefore not yet visible to students) be sure to click "Save & Publish" instead.