A .rar file is a compressed archive. What you use to open it will depend on your operating system.
The typical method is to use WinZip on a Windows system. Windows10 does not need WinZip. MAC systems have an Unarchiver program.
Other archive programs can be used ex. 7Zip and there are others.
A Google search for RAR files will give you details on how to extract the contents of a .rar file
Robert, I have Win10, when I click the file, it asks what program I want to use, the only choice is to look in the app store. Thanks.