Download and install Skype onto your Mac if you haven't already done so. Launch Skype once you have finished the installation process.
Transfer your contacts for Apple's chat client iChat into your Skype contacts list to converse with them via Skype. Since both iChat and Skype are instant messaging clients with video calling capabilities, you don't need to install anything onto your computer to be able to use Skype if you already use iChat. Your iChat contacts need only approve your having imported them into your Skype list for you to chat, voice or video call them using the software.
Click on the "Contacts" drop-down menu and select the "Import Contacts" option. Press the "Apple Address Book" tab.
Type in your Apple credentials, which are the same user ID and password you use to sign into iChat. Click the "Import" button.
Select the name of each iChat contact listed in the Skype window to send each a Skype contact request. Once a contact approves the request, he appears in the contacts list for Skype.