This is how the consulate defines the qualification for the visitor visa grant:

“Applicants for visitor visas must show that they qualify under provisions of the Immigration and Nationality Act. The presumption in the law is that every visitor visa applicant is an intending immigrant.
Therefore, applicants for visitor visas must overcome this presumption by demonstrating that:
The purpose of their trip is to enter the U.S. for business, pleasure, or medical treatment.
That they plan to remain for a specific, limited period.
That they have a residence outside the U.S. as well as other binding ties which will insure their return abroad at the end of the visit.

All visitor visa applicants require to be interviewed at a US Consulate, before being granted a visa. Applicants need to appear in person for the Interview at a US consulate. A prior appointment is must for this purpose.

Process

1. Sponsored Trip: If applicant’s has child or relatives lies in USA, they can sponsor the visa for the applicant.
Sponsor: Any US based person can sponsor visa for his/her parents, relatives, friends.
Liabilities of sponsor: Sponsor needs to provide affidavit of support form stating and assuring to take the liabilities of expenses required for applicant’s trip.
Other then this they also need to provide some other documents required to support their claim as sponsor.
Sponsoring does not guarantee the visa grant. Individual applying for visa must meet the criteria, set for US visitor visa.
2. Self Sponsored: You can be a self sponsor for your trip. You must have sufficient funds and proof of financial capability that can justify your trip expenses.