19-08-2012 15:13 - edited 19-08-2012 15:13
Skype-to-Skype video calls are indeed free, but calls to phone numbers are not free. You need to add other Skype users to your contact list and then start a video call through the contact list.
See this FAQ for how to add a Skype contact:
This FAQ, while titled for the iPhone and iPod Touch, also applies to making a video call on the iPad once you have the person you want to call added as a contact: