First you must add contacts (the people you wish to speak to). If they have a skype account, ask them for their skype name. Then you can go to Contacts-->Add Contact and type in their name. If you add them, they will receive a contact request, which they will accept if they know you.
Once you have contacts, all you have to do is click their name and select "Call", and you can talk with them over Skype for free. You should be able to speak with any contacts you have regardless of their location.