There are a few options:
1. Download WinRAR
You can download WinRAR from here.
However WinRAR is not free, and will continually nag you to 'register' it. Besides that, you will also receive a lot of functions that general computer users do not need. However, if you prefer installing a comprehensive and extensive shareware to extract your RAR, ZIP or 7z archives, WinRAR is the way to go.
2. Download WINZIP
WinZip is similar to WinRAR in a lot of ways, however, once again, it is not free. As you can expect, nag screens, reminders and other sorts of ways to get you to purchase the full version will occasionally come up. But WinZip is an extensive program, that does the basic needs of extracting ZIP, RAR and 7z files, but also integrates extensively in to your context menu even when you right click on files that are not extractable.
3. Get uZip
XetoWare has simplified the extraction process in to a simple, but powerful freeware called uZip. uZip unzips not only RAR, ZIP and 7z, but also less common archives such as gzip, tar, and ISO. On top of that, uZip does not nag you or interfere with your system's context menu: it really is a lightweight utility designed for those who just want the files inside the RAR, ZIP or 7z archives! Download uZip here.
So there you have it. Three ways to extract these different types of archives. We personally recommend you to use uZip if you just want to extract the files and move on with your work. However, WinZip and WinRar come in useful when you want to perform extensive actions such as Zip and email files, repair archives, etc. It is just a decision on if you want to purchase their full version after the trial periods expire.