Rar files are archives similar to WinZip but since they use a different compression algorithm technology, they cannot be opened by WinZip or the default zip utility provided by Windows XP and Windows Vista.
What is a RAR File?
RAR is the native format of WinRAR archiver. Like other archives, RAR files are data containers, they store one or several files in the compressed form. After you downloaded RAR file from Internet, you need to unpack its contents in order to use it.
Opening / Viewing .rar Files
In order to open .rar files you will have to download WinRar which holds the proprietary rights to the format. WinRar though is a paid and you will have to buy a license from them after the trial period expires.
7-Zip on the other hand is a free file archiver, which also supports the .rar format, 7-zip is also a open source software which we had earlier included in the 35+ amazing and free softwares.