Dear Riyaz,
As Mr. Ashish has told you, Public company can go to public for issuing shares. They can arrange money from public in the form of issuing shares while private company has to arrange by their own. They can not go for public offering.
Unlike private companies, public companies have to public their revenues and publish their annual reports and accounting statements like Profit & Loss Account, Balance Sheet and Cash Flow Statement and have to make it public.
There are other differences also regarding minimum number of directors 2 and 3 and like that.
thanks & regards,
Krishna Sati