To start using Skype's video calling functionality with a Facebook account, users first have to link their two accounts together. This can be done easily from within the latest version of the Skype desktop application, free to download from the Skype website. To start chatting, users click on the 'view' tab, and then select Facebook friends. From there, double-clicking an online friend's name will bring up the standard text chat box, and clicking the 'call' tab brings up the option for a video call, which that person then receives through Facebook. Simples.
The addition of Skype video calls to Facebook is another step in the two services' partnership, which started with Skype adding its users Facebook friends to their list of online contacts in the Skype desktop client.
Still unclear on exactly how it works? Take a gander at Skype's official video below.