In the past we have told you How to Open or View RAR Files. RAR files are similar to Zip files, however they use a different proprietary compression algorithm which is why they cannot be opened by Windows or by using WinZip.
In order to open RAR files you will either require to download WinRAR software from RAR Lab here http://www.rarlab.com/. Though the software is paid, you can continue using even after the time limitation is over.
You can also use a website to Open zip and RAR files online, however the above software are free to use and do the job so you might not even require to use the online option.
In future you can also use a software called OpenWith to find out which application can be used to open unknown files.