Look for Lawyers do US visa

Why would you need a lawyer?

Fill out the application, pay the fees, and maybe do an interview. I know it is a complex set of processes but there is no requirement to use a lawyer.

For tourist: https://travel.state.gov/content/visas/en/visit.html

For business: https://travel.state.gov/content/visas/en/business.html

Main page for visas: https://travel.state.gov/content/visas/en.html

Best of luck.

I did all the paperwork for my wife's immigration and while it does not require a lawyer, it was an awful lot of work to get everything right.  One problem was agencies asking for things that were not in their own instructions.  The last one for us was the Vietnamese employee at the consulate asking for my wife's house book even though the consulate website did not list it as a required document.  Fortunately I was with her and asked to speak to a US employee.  When I addressed the situation to him, the problem disappeared but I know that other people were unfairly sent away that same day for that very reason.

SophieTran276:  You have not indicated but I would guess you are looking for a student visa.  I have a Viet Kieu friend in HCMC who was a paralegal (legal assistant) in California and who has a small business assisting people with US visas.  If you like, send me a private message and I will give you the link to his Facebook page.

Mark Ellis has been assisting with visa applications here in Vietnam for a  very long time.   http://www.marcellislaw.com/