Embeds are a great way to include content from third party websites. Depending on the website, they display as an embedded block in your newsletter. It is up to the website owner to describe how they want their website embedded. Most interactive websites provide for this, however if they don't you will see an error when you try adding the embed.
To insert an embed
Click inside the article where you'd like the embed to appear
To the left of the flashing cursor will be a grey '+' button - click this
From the menu that appears, click Embed
A popup window will appear asking for the website URL. You can either paste the URL to the website, or if you have an embed code (starts with <iframe>) you can paste that as well
Press the Insert button and assuming the embed platform was able to retrieve content from the website, you'll see the embedded website on the page
To delete an embed
Find the embed on the page you wish to delete
Click to select it, and press backspace on your keyboard