Simply check off the folders or individual files you want deleted and use the menu 'File|Delete all Checked Items' or the wastebasket icon on the toolbar to remove them.
You can add your own folders with the menu 'File|Add a Folder' or the open folder icon on the toolbar.
You can remove the folder you have added with the menu 'File|Remove a Folder' or the X icon on the toolbar.  This does not delete the folder contents, it only removes that folder from the treeview.
Clicking on files will open them using the associated program on your system, if such an association exists.  Excel spreadsheets will open in Excel, web pages will open in your browser, etc ...