Skype is proprietary software that allows you to make calls over the Internet using your computer. Skype uses decentralized peer-to-peer technologies, so your calls do not go through a central server, but through distributed servers and other users. It uses its own proprietary communication protocol to achieve this. In addition, all communications are encrypted from end to end so that others cannot listen in. The Skype software is free to use, but it is not free software; the source code is proprietary and not available for modification.
Install skype in Ubuntu
First you need to edit /etc/apt/sources.list file from your terminal
gksudo gedit /etc/apt/sources.list
Add the following line
deb http://download.skype.com/linux/repos/debian/ stable non-free
Save and exit the file
Now you need to install GPG key
sudo apt-key adv --keyserver pgp.mit.edu --recv-keys 0xd66b746e
Update source list
sudo aptitude update
Install skype using the following command
sudo aptitude install skype
Using this repository, you will automatically receive future updates to the software
To start Skype, choose Applications->Internet->Skype.