You'll need to buy Skype Credit or a subscription to make call international numbers on skype. Steps to call international numbers from Skype:
1. Skype login
2. On the toolbar, select call-> select Call Phones
3. Select the country you need to make a call to from the drop-down list. After selecting the destination country, skype will automatically charge you a fee
4. Enter the number you want to call.
Or you can also enter a country code manually. To dial country code Angola, You will enter + 244, click and hold the 0 + button for two seconds on the Skype dial pad, then release; the + symbol appears in the Enter number box.
5. Click the blue call button.