TL;DR (Too long; didn’t read.)
Files with rar suffix are compressed archives made using any of the WinRAR or RAR compression software.
Long Overview
RAR stands for Roshal Archive and it is a proprietary archive file format that supports error recovery, data compression and file spanning. It was developed by a Russian software engineer Eugene Roshal. RAR first introduced in March 1993. RAR is the native format of WinRAR archiver. Like other archives, RAR files are data containers, they are simply a collection of one or more than one files/folders in compressed form for easily transportation. After downloading RAR file from Internet, you need to unpack or decompress its contents in order to use it.
This file format belongs to Compressed or aggregate files category
Below listed software supports rar file extension
RAR File Extension is developed by Eugene Roshal Initially Release in 1972. RAR is not a Open Format File or Free File Format, its a proprietary archive file format but the decompression source code is available, but it's not free software due to the restriction that it must not be used to reverse engineer the RAR compression algorithm
application/x-rar-compressed
RAR archive version 1.50 onwards - 52 61 72 21 1A 07 00
RAR archive version 5.0 onwards - 52 61 72 21 1A 07 01 00
Using any third party software: RAR File Extension can be opened Manually using any third party software listed above like 7-ZIP or WinRar and there are lots of others, that come for free/paid. So, it all depends on your choice. After downloading and installing the software just double click on the rar file and that's it. (Make sure to enable the shell integration)