i would like to know how to install any software like avg free for linux without using add and remove program...
please help me!

Ubuntu is Debian after all.

Thus provided that you have a .deb package and that it is in your path (the easiest way is to put it in /home/yourusername), do as following:

Open a terminal.
sudo dpkg -i "packagename" (without quotes).

See also here:

http://www.newlinuxuser.com/howto-use-dpkg...tall-deb-files/

Another easiest way is to download the .deb and then double click it.