Product design?

Even i have no little bit idea

Then its best that you start with the very basics and work up from there (it is a very large field).

http://en.wikipedia.org/wiki/Product_design

http://www.google.co.nz/search?client=firefox-a&rls=org.mozilla%3Aen-GB%3Aofficial&channel=s&hl=en&q=product+design&meta=&btnG=Google+Search

Add additional search parameters for more detailed information if you have general questions on specific relevant topics.

Go and make a cup of coffee.
As soon as you touch any item, spoon ,jar, kettle etc. stop and examine it in intimate detail, as yourself the following.
Why is it the shape, size it is?
Does it fulfil it's purpose?
What is the material and why?
How was it made? If it is a plastic moulding look to see how the mould tool opened and closed, by looking for the split lines, the injection points and the ejector marks.
Is it a 'new' shape/design?
Are the design, material and method of manufacture compatible and cost effective?
Could you improve on it?

Are you getting the idea?
Design is about opening your eyes and enaging your brain and your imagination.
If you do the above task carefully, taking items apart if necessary, then you should finally get your coffee in about 3hours.
Del

thnak you so much.i have a idea now

in the design wht is the first step?is it making 3D?

It's engaging your imagination.
How you turn it into reality is entirely up to you, I'm a great believer in making prototypes and experimental models as soon as possible.
A 3D computer model and stereo lithogrophy are only any use if you have the idea in your head....
Personally I find a pencil and paper is often my first step at expressing my ideas. Or talking and waving my arms

It is still slow and cumbersome to be creative on a computer, a pencil is so much quicker. I see a computer as a drafting aid rather than a creativity aid.
Del