Email broadcasts are one-off emails that you can send to your subscribers. They are found under Marketing >> Email Broadcasts.
Create your first broadcast and you'll see that you can segment your broadcast to your subscribers based on their subscription status and subscription plan.
Once you've picked your recipients, you can pick your settings for the email:
Email Preview Text is a short snippet that some email clients show beside the subject. You don't have to set anything here but most email clients will use the first part of the body text if you don't specify anything here.
Next you can write your email:
Finally, click Preview and send to get a preview of your broadcast before sending it to your users.
You can track open rates on the email broadcast list page:
If you want to track more specific stats on links clicked, make sure you're adding UTM parameters to your links and have the Google Analytics integration installed wherever your links send your users.