It is free if you call skype to skype. You need credit or a subscription if calling landlines or mobiles.
Downloaded the app on my ipad. When i try to make a call, it tells me Ihave to purchase credits. Its not free?
some Skype services such as Skype-to-Skype calls, conference calls, chat and group chat, 1-on-1 video calls are indeed free of charge. However, some services such as Skype-to-mobile/landline number, group video calls, voicemail, SMS, online number, etc requires credits or subscriptions.
The support/user guide section offers a mode detailed descriptions - https://support.skype.com/en/
Are you going through your skype app? Have you accepted the person so you can place him in your contact list? Let's say I want to call you on skype I have to first send you a message for you to accept me as a skype contact. If you accept me I can call you for free as you are in my contact list or you can call me. Have you done this? I have never been charged for a skype to skype call, and I use it daily.