Question on RAR files

I'm sorry to bother you all but I use Photoshop CS3 and I download brushes/textures for my icons from time to time but I've noticed that some people are saving their brushes/textures as RAR files and I'm not sure how to access them.

I tried the memories and I couldn't find anything and I tried Google and I learnt that I need a RAR unzipper but beyond that I got confused. Can anyone point me to a free RAR unzipper or give me some advice please?