The System Folder is the heart and soul of the Macintosh. It can easily be found by double clicking on the hard drive icon. Inside the system folder are all of the files the Macintosh requires for operation. Extensions For beginners, it is only necessary to know the general purpose of Extensions and how they fundamentally work. Extensions are really miniature programs that tell a Mac how to perform certain functions.
Extensions are often specific to a program, but can alter the operating system as well.
Without extensions, a Mac could not perform many of the activities it does. As a Macintosh starts-up, a series of little icons appear on the bottom of the screen. These icons are the extensions being activated by the Mac. Extensions can ONLY become active on a Mac if they are loaded at the time of start-up. In general, the user rarely has to worry about extensions and beginners should never move them around unless they are confident that they know why and what will happen once the extension is removed from the extensions folder.