See also 10 Steps to Getting Your Visa: http://www.yourimmigrationcenter.com/visasteps.html.
I added this information to the page, because you always start with a visa first, before you start your Green Card process. Exceptions are: Winning a Green Card in the DV Lottery or in special cases where you are allowed to stay in the United States without having a visa, e.g. Asylum etc.
Broad Overview/List of Visas: