If you wish to communicate over the internet using video then you will need some kind of video communication tool. Mac OS X Lion comes with an application called FaceTime that allows you to easily communicate without the need of other devices or software.
It is an application for making HD video calls.
Macs with built in cameras, the iPad 2 (and later), the iPhone and the iPod touch all have FaceTime capability.
An Apple ID is required to use FaceTime on the Mac.
Windows PCs are not able to use FaceTime and you would need to use an alternative such as Skype.