There are multiple ways to filter the data you see:
Filters in the left panel
You can select either a particular one, all, open or done Epics.
Filters in the list of Epics
By clicking on the numbers at the top row you can filter to see:
All issues
Unestimated issues
Unassigned issues
Completed issues
Sorting of the data
You can sort the displayed data per column by clicking on the name of each column.
Issue Details
Click on each epic to see a list with all tasks and sub-tasks in it. You can then investigate each one in detail and see its status.