Most of the universities ask you to submit affidavit along with all other documents when you are applying to the school. Some schools ask you to submit affidavit after declaring the admission. They will give you I-20 only after submitting affidavit.
You can sponsor by your own or your family or relatives in Pakistan or abroad. Some times it may be your employer or a organisation.
Is affidavit and bank statement same?
No. They are different.
Who will give affidavit?
Notary Lawyer. Both sponsor and lawyer have to sign the affidavit document.
A 20 rupeee stamp paper is enough.