I want to learn C language (is this something good ?) and i didn't know from where i can download the language to my PC ? and are this FREE or must pay for ?
Is C a good language? Definitely. Is it the best first language? Depends.
If you are using Windows, you can download Visual C++ 2008 Express Edition SP1 from Microsoft for free.
On Ubuntu, just run
sudo apt-get install build-essential
On Mac OS X, install Xcode from Snow Leopard/Leopard DVD (or download the latest version from Apple developer Web site)