Every section of the page has a 'New' button at the top center of it.
Clicking on this button reveals a list of all built-in components (about us, contact, embedded video, etc.) you can add to the page.
When you've located the component you wish to add, click it. It's automatically added to the page. You can then move that section up or down the page by editing the page structure.
Find a specific type of component
When you click the 'New' button you can then specify which type of component you're looking for. For example, if you want to add a video, click the 'video' link.
A list of components that offer this feature is listed. In this example a single component shows since only one component is available for video.