To create your first Broadcast, go to My Audience and choose broadcasts & automation 

Click to create a new one

After you create it, you will be able to customize your outgoing email, and add an audience segment who should receive this automated email. 

This means you should previously create your desired audience segment. To see how it's done please check out this article here -

Creating an audience segment means you can choose any specific category of your audience and send them an automatic email. 

For example you can set that everyone who watched over 50% of your video will receive an email.