This is an overview of the visit evolution.
It is broken down into various reports, which are displayed in sparklines at the bottom of the page. You can enlarge the graphs by clicking on the report you'd like to see.

Visits: If a visitor comes to your website for the first time or if he visits a page more than 30 minutes after his last page view, this will be recorded as a new visit.
Unique visitors: The number of unduplicated visitors coming to your website. Every user is only counted once, even if he visits the website multiple times a day.
Actions: The number of actions performed by your visitors. Actions can be page views, internal site searches, downloads or outlinks.
Users: The number of users logged in your website. It is the number of unique active users that have a User ID set (via the Tracking code function 'setUserId'). (User ID)
Actions per Visit: The average number of actions (page views, site searches, downloads or outlinks) that were performed during the visits.