So far as I know, there are several visa categories in the USA. The most common among Nepalese is Student (F1) & Tourist (I dont' know the category B1/B2 or so).

There are three basic thing US wants you to show (it does not mean you have to have all those :) in many cases )

- Genuine motive to visit USA
eg. I want to go to USA to get an MBA degree in finance

- Proof of fund to support your stay in USA
eg. My university will pay me $ 8000 /year, my father will send another $18,000/year

- Reason to return after completion of your motive.
eg. I will run my dad's fishery after I return :

Once you know what they want you, can start by yourself (clue: find a university to apply)

Good Luck.

Disclaimer: Fee immigration advise can be dangerous. You are the only person solely reponsible for your deed.