The Email Tools lets you keep in touch with your customers in a variety of ways. When you launch it from the Pro Control Panel, you are greeted with the following window.
As you can see, this window is designed to be self-documenting, with generous help texts and tooltips to guide you along. For instance, once you filter a set of email addresses to send messages to, you get the following message about what kind of email templates you can use.
Since sending potentially large number of emails is usually frowned upon by the recipients, the Email Tools warns you about it multiple times and makes you jump through some software hoops (confirmation dialogs, test emails etc.) before you can actually send out bulk email.