The file list contains a list of the files inside your selected zip file.
To select a file, click on it. To deselect, click again. To select a group of files, simply drag the mouse over the region. You can also use the keyboard and press "Enter" to select/deselect files.
To view a file, double click it. It will be opened in its native program, if it is a document. If it is a document and you make changes which you save, you can apply those changes into the zip file automatically - the Studio will ask.
To ascend to the previous level on the hierarcy, click View->Back One Level.