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, and pay as you go with your credit card or get a monthly subscription for the best rates. Download the app to your Nokia Lumia phone.
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).