That's fairly vague.
Every camera has it's own communication.
It is entirely different trying to control a Nikon from a Canon. And each model within one maker can be different.
Just saying it is connected to the PC doesn't help either. It could be USB, Firewire, a proprietary interface, an older SCSI camera,
Webcams are a bit more standardized. They talk to the OS, you talk to the framework, and it doesn't matter as much what brand of camera is connected. Some support special features like auto-adjust lighting, some don't... some support a higher resolution still shot, some don't so you have to take just one frame out of the video stream.
Doing a google for "Canon SDK wrapper" will find you articles like this
http://www.codeproject.com/KB/audio-...a_wrapper.aspx
where someone has written a .NET wrapper around the Canon SDK.
If you have a different camera in mind a similar search might help.