C-Form - What is the use of that Form? & Where it will be used?

I need C-Form Format. Can anyone help me to provide that form? What is the use of that Form? & Where it will be used?
I didnt know about that Form.... I purchased one material from one of the clients with the VAT instead of CST. Now they are asking C-Form. What will do for that?

HI Deeparaji
To get C Form you should have valid CST registration with Sales tax department & those products should have listed in the commodities list. First just check whether you have CST registration ant that particular commodity is listed. Any doubts do reach me. :)

Hi Deepa
Even if you have CST registration is that product/part is listed in the commodity for CST? If so then you should approach to Commercial/Sales tax department. C Forms are issued in Sales/Commercial Tax department.
If you can tell me your location then I may give some inputs. For ex in Karnataka you shall apply the same over online. Once you get approval then take that C Form to the department and just get seal on that. You should also get the signature of the authorised person in your office.
Before that you should have even declared into interstate purchase of the same commodity.
:)