Presents the 'open file' dialog from which files can be selected for opening. 

The default file type is, of course, Excel, but many file types can be opened using the 'files of type' drop-down in the dialog (Above).  It should be noted that if the file is text of a type '*.csv', (comma separated value), it will open automatically in Excel, as any normal Excel file.  If this is undesirable and your intention was to invoke the 'text wizard' then you should rename the file with a *.txt (text file) extension, or remove the extension all together and open the type 'all files *.*' More detail on getting text (and other external data) into Excel can be found here.

nb: The GetOpenFilename method of the application object purely collects the file name.  It does not open the file.  You use the string value returned when the dialog is closed to open the file. (see example)