The Overview tab allows you to see data referring to your site across a selected date range (as selected using the Controls menu). This tab is designed to give you an overview of how your site(s) is performing before heading to the following tabs to dive deeper into the data.
Key data you will find on this tab:
Active Users
New Users
Current Users
Visitors (if applicable)
Activity information and breakdown (Comments, RSVP's, Likes, Actions per User)
User Retention