At the top is a combo box for selecting the drive. Below this is a list of folders - double clicking on any of these will switch to that folder. Below this is the list of files in the current folder - double clicking any of these will cause that file to be opened. Finally, at the very bottom, are a pair of radio buttons enabling you to select what sort of files are shown: Rich Text Format files only, or files of any type.
There are several ways to select multiple files in the file list:
You can then open the files by using the right mouse button and selecting the "Open File(s)" item from the popup menu. There are also options in this menu to delete file(s), create a new folder, or to add the current file(s) to the Favourites list.