First apply for I-20. When you apply for I-20, you'll be charged US $25 by universities in USA which is non-refundable. Universities might not accept your request for I-20. But if they accept, they'll send you an I-20 which you'll need when you apply for American Student visa at American Consulate's office.

If you find this process difficult you can also take help from educational consultancies in your country. They can assist you for complete studying process in United States. Some educational consultancies from Pakistan are found to serve students in each and every studying abroad process.