[ubuntu] How to install Winrar

Hello!
I'm new and want to install winrar on ubuntu. I have downloaded the linux version of winrar but don't know how to install it.
I have tried two terminal commands:
"sudo aptitude update && sudo aptitude install rar unrar"
(computer didn't find the command)
and "sudo apt-get install unrar"
(computer said that he can't install unrar"
What have I done wrong?? It's the first time i'm installing a programm on ubuntu.