Each class is shown as a card. they show how many students are in that class and show upcoming tasks. Click on the title of the class to open it.
At the top of the page, you'll find the hamburger menu (the one with 3 lines). Click on it to open it.
This is where you can access a version of your Google Calendar which shows upcoming tasks. You can also access the To Do page, which lists upcoming tasks and their current status. You can also access archived classes from here (not shown in the screenshot).
Clicking on "To do" will open the to do page, which shows you the tasks to review and that have been reviewed.
This is linked to your normal Google Calendar, but here only shows you taskes that have been set with a deadline line.