This is a Video & Text block. Click on this text to start editing and enter your own text with some basic formatting. Just click anywhere outside the text box when you're done to continue working on the rest of your page.
Hover your mouse over the video opposite to show the Video Settings button. Click on the button to open the Video Settings window where you can enter the address of a YouTube video. Just copy and paste the URL of the page on YouTube and you'll see a preview of the video straight away. Click the done button and it will be added to your page.