For the youtube video, click on "share" then click on "embed". Then you should see this screen
Copy the link inside "src". Make sure you're not copying the WHOLE thing. The link should look something like "https://www.youtube.com/embed/..." The simply paste it in the Images & text editor in the app, as shown in the following screenshot. You may need to put in a width.
That's it! You should see the following.