here i want to know about how can i use mobile cam as webcam?

clearly not an intro, and you've not even said what your hardware is, what linux distro you are using etc... moved to Linux - Newbie. also you didn't say please / thankyou

By connecting it either wirelessly or with a wire to your operating system, where you need to have a piece of software that is able to communicate with the "mobile cam" (and the mobile cam must be able to send it's data over the connection as well), so in the end both ends are able and willing to transfer information between each other.

After that..well, it depends on the hardware (it's capabilities), software (if there exists software that is written to work with your hardware) and such things. Unless you specify them, it's pretty difficult to give better advice than "connect the camera to your computer and see what happens".

I would be *assuming* that they meant a mobile phone... may well be wrong.