WinRAR is a competing product to WinZip; both products compress/decompress and archive files. Files compressed with WinRAR typically have the .rar extension, as opposed to .zip for WinZip archives. WinRAR can also create and decompress a WinZip archived file.
Like later versions of WinZip, WinRAR has the ability to create archives in multiple parts; that is, it not only can compress a file but can split it up into smaller parts. In WinZip, this is called a “split Zip file”; in WinRAR, this is called a “multipart” or “multivolume” archive. When this is done, the extensions for the smaller RAR files end up being .r00, .r01, and so forth, with the first file just having the .rar extension. To decompress a multipart archive, you simply have to ensure that all the component files (.rar, .r00, .r01, etc.) are in the same directory. When you double-click the .rar file, all other files are automatically found by WinRAR without you having to select them, and the final decompressed file is automatically assembled from all those files.