This graph shows the daily traffic on your site over the last 30 days. Each bar represents one day, and the bar's height represents the total number of visitor sessions on your site during that day, regardless of whether these were first time visitors or return visitors (the exact number can be read at the bottom of each bar).
Important Note : by default, your account is set to 'test mode' in which a visit is counted every time your page is loaded. If the same visitor reloads your page 5 times in 30 seconds, then 5 visits will be counted (this is done to allow you to test the counter after installation). In order to get more meaningful stats, you should set your account to count 'visitor sessions' by selecting 'Type of Tracking -> Visitor Sessions' in the Control Panel. This ensures that a visitor loading your page several times in a row during the same browser session is only counted once (if that person comes back to your site 30 minutes or more after leaving it, a new visitor session will be counted).