The "Open Files" are is where you will find a list of the workout files that you currently have open. Initially, you will just see the three Tabs across the top(Athlete home, Calendar, Chalkboard)  To open a workout, click on the Calendar page and then double-click on a workout.

Once a workout is open you can move between the tabs and also create ranges, zoom in on data, etc.  If you see a '*' to the left of a workout date, this indicates unsaved changes have been made to that workout.  Be sure to save that workout.  To access more information about a workout, see the four tabs across the top of the workout area (Journal/Graph/Quadrant Analysis/Scatter Graph).  To close a workout, click on the 'X' in the upper-right corner, next to the 'Options' link.