how can i open a rar and install

i just bought mac OS X a week ago and i downloaded all the sims packs and i can't install any +_+
 i'm new to the mac world ive always used hp or sony so i really dunno whats the trick to open a rar on MAC
i tried to download rar but didn't work, i know how to install on any other laptop no problem and how to fix my own sims but on mac its a whole different story cz ive never used one before 

so can anyone gimme a tip here on how to open a rar and how to install on mac OS X 10.8

You need to use Stuffit, follow this guide!

Shamrock wrote:You need to use Stuffit, follow this guide!

 thank you so much

Sure!
Any problems left?