In the second section of the campaign reports data Mailchimp tells you how many emails were successfully sent. This is just a precaution that Mailchimp takes to confirm that you are not just spamming people. If you got your list the right way this number should always be above 90%, but if you got the list the wrong way then you will notice that this number is much lower because there are many fake email addresses. On the left of number you will see the Clicks per open number (this is the number that email services like Constant Contact give by default. Instead of clicks per emails sent it is a much higher percentage. The rest of the data is not so important. But the graph underneath it can teach you a lot about your list.
The chart is a graph of the opens 24 hours after the email was sent. If you look at several emails charts you can start noticing patterns like when people most likely open emails, when then never open emails, when the best time to send the email is. Every few emails make sure to compare these charts to see if things change, it can teach you a lot about your audience.