Go to your publication dashboard and click Analytics. You'll find two tabs there.
Overview shows your views, readers, and subscribers, plus your top posts by views. Pick a time range from 7 days to a year. The default is 30 days.
Audience lists everyone who subscribes to you and when they joined. Supporter counts are not shown yet, because paid subscriptions are coming soon.
A few tips for reading your analytics:
Readers vs views: readers counts people, and views counts visits to each post. One person who reads three posts is one reader and three views.
Look at your top posts over 30 or 90 days, not 7. A post's first week tells you little. The ones still being read weeks later show what your readers really come for.
Your subscriber list is yours. These are people who asked to hear from you, and they're worth more than any number of passing visitors.
Cantabook doesn't count likes, follows or shares. Your analytics are there to help you understand your readers, not to turn writing into a popularity contest.