how to install yii frame work on your system:
1. go to Yiiframework.com, navigate to download page. http://www.yiiframework.com/download/
2. download the source code.
3. unzip it and rename it as yii.
4. move that yii folder to your local host directory(in my case it is /var/www)
5. now go to terminal get into your local host root directory(www) and enter this command.

 root@satya-OptiPlex-9010:/var/www#  yii/framework/yiic webapp sample-app

6. It will ask for confirmation, say y for yes.

That's it....
your sample-app is ready.

now go to browser and type localhost/sample-app/
it's that simple...