You can use your phone to make Skype-to-Skype calls or send Skype-to-Skype instant messages. With Skype global rates, you can also call landlines or other mobile phones. You can also make video calls and pay as you go with your credit card, or get a monthly subscription for the best rates.
To download Skype, tap Store or go to http://store.nokia.com/.
For more info, see the user documentation on the Skype for Windows Phone support site at https://support.skype.com/en/category/SKYPE_FOR_WINDOWS_PHONE.
For more info on Skype-to-Skype calls and IM, see the video at http://www.youtube.com/watch?v=AF2HRYdPnAM (in English only).