Summary: Has Cards that summarize the other sections, such as Audience Summary, Post & Engagement Summary, Performance Summary, Reach & Impression Summary.
Audience: Shows Cards that graph the trends of how your audience interact with your posts. You will see Cards like Page Like Growth, Page Likes by Country, Page Likes by Age Group, etc. which indicates how your audience is reacting to your content and the demography of your audience.
Posts & Engagement: Has Cards that show what type of posts are working, your best posts in that period, your top fans etc. Some Cards you'll see here are Number of Posts vs Engagement, Top Posts, Top Connections, Best Time to post, etc.
Performance: This section shows how your Facebook Page has performed over that period. It has Cards such as Page Views, Page Clicks, Postive and Negative Feedback.
Reach & Impression: Shows how your posts are reaching other feeds and the engagement they receive. For example, there are Cards like Organic and Paid Page Impressions vs Reach, Viral & Non-viral Page Impressions vs Reach, Page Shares and such.