The Classes tab of the course Analytics page provides aggregated student participation and engagement data for each class in the course. There is a bar-graph at the top for "at a glance" perspective on each class and a more detailed grid-view of the data at the bottom.
Each bar in the graph is a class, and each row in the grid is a class. Data is only shown for classes that have already happened or those with no date/time. As classes occur (their date/time passes), they are added to the data on the page (both as bars in the graph and rows in the grid).
This data is updated throughout the day, at least hourly but typically a few times an hour. So while student interactions may not show up immediately, if you are waiting for class data to update, you should not have to wait long.
You can SORT the data in the grid by clicking any of the column headers, or you can export the Class data shown (along with other fields) for reviewing in detail offline. See Definitions of Analytics Data Metrics for detailed definitions for each of the data fields/metrics.
Hover your cursor over a bar in the graph to get a quick-view pop-up of the participation data for that class, as shown in the below figure. 
In the Grid at the bottom of the tab, click on a class to see detailed Student analytic data for that class. A popup window appears listing all the students enrolled in the course and showing their activity in the selected class, as shown in the below figure. 
The bottom of the popup window shows how many students are shown on the page provided in the window. It also provides arrows for you to page through the list of students as needed. The above figure shows a course with 30 students enrolled, all appearing on Page 1 of the popup.
Like with all other grid data on the Analytics tab, you can click the headers of the table to sort by the selected column, in ascending, descending, or return to the original order.
Click CLOSE when you are finished reviewing the detailed student data for this class.
Analytics for LIVE classes - Viewing data for Live Streamed Classes is only gathered from Universal Capture devices and is a little different than for VOD classes in some areas. See the following sections of the Definitions of Analytics Data Metrics page for more details: Attendance Percentage, Video View, and Video View %.
Missing Live Data? As mentioned in the above note, analytics data is only gathered from Live Streamed Classes performed on Universal Capture devices (Pro, Pod, or UC software installations). If you believe you are missing analytics, this is most likely the culprit. No analytics data is gathered from Live Streamed Classes done on legacy SCHDs.