Hidden files are those which begin with a period. By default in the Mac, these files are not shown in the Finder and in the File -> Open dialogs of many Mac programs. If you need to edit a hidden file in the Mac, and you want to use the default Mac text editor (TextEdit), here's is a trick that will allow you to do this.

Open a terminal window (Applications -> Utilities -> Terminal). Using the cd command, change to the directory that contains the hidden file you want to edit. Once there, type open -a TextEdit .fileName where .fileName represents the name of the file you want to edit. This command will cause a new TextEdit window to open with the contents of your hidden file in the editor.