On the web, simply hit the e key. That will open your default email application and create an email with the headline and link you want to send.
In the iPhone/iPad app, if you're viewing the feed list, simply swipe the story headline to the left, and you'll see a menu of icons. Touch the share icon, and then choose your mail app. if you're viewing the item itself, simply touch the share icon in the top right of the screen.