First of all you have to get the latest release of Skype. Link to download page
At the moment there are three choices to pick for download. Choose the one that matches the type of architecture your OS support 32-bit or 64-bit software. Even though the one’s listed are for 8.04 & 8.10 versions of Ubuntu, they will work for both 9.04 & 9.10.
When you choose the one that will work for your system. Choose to save the file to the Desktop, or where it is most convenient for you.
The full article is here
Just check out our list of Getting started with Ubuntu in the Linux – 101 at the top of the page.