ARC files are created by one of many arc programs. Several different arc programs have been written to combine multiple files into one ARChive file. ARC files are less common on the Internet lately due to the newer ZIP and EXE formats. The problem with ZIP files and many other archiving methods is that you need the un-zipper program and possibly the latest version of that program before you can get access to your files. Let me see if I can make more sense of this.
All self extracting files are EXEcutable.
This program then looks at the rest of the data in the file and pulls out the archived files that you wanted in the first place. But you are better off doing some of the decision making yourself rather than letting Netscape take care of it every time. This will open up a dialog box that among other things will allow you to select where you want to save the file. Usually you won't need to change the filename as listed by the server that you are accessing. That will show up, highlighted, in the top line of the above dialog box.