Once admitted to a US graduate school, they will require supporting documents to prove that you are able to financially support yourself while studying in US, before they send you your I20. Which means that you have to show enough funds to cover two years of expenses that include tuition, living and miscelleaneous.
You may need to send bank statements, bank loan approval letters stuff like that to prove you are financially well off to pursue your studies. Once these documents are received school will send you an I-20 which you can use to apply for F1 visa.
Here is a sample of : AFFIDAVIT OF SUPPORT for school.This should be notarized.
This affidavit of support can be signed by more than one person in your family.I had mine signed by my brother & father.
Include all the financial paper required to show enough funds such as:
Bank statements,Bonds, Bank loan papers, insurance papers, provident fund statement, any financial paper that can be used to show that you have enough funds.