Iframes are a common way to display content like videos from Youtube and Google calendars.
To embed a youtube video in your page follow these instructions:
Use the youtube site to find the video you want.
Click the 'Share' button below the video.
Click the 'Embed' button next to the link they show you.
Copy the iframe code given.
Open your Joomla page in Edit mode
Click on the button for the "Source Code Editor" <>, it is located next to the "Printer" button, underneath the "Font Size" field box.
You should now be in code view. Copy and paste the iframe code obtained from the source site into the desired location in the page.
Click on "Source Code Editor" to return to visual mode.