Upvote:2
Depending on your visa classification you can add (note that the adding is done by the consular officer through the issue of a visa to your dependent, you don't personally physically add them yourself) your dependents to your visa. For visitors visas you cannot add them and they essentially apply as fresh individuals on their own merits.
For H1B and other employment based visas etc, you do that by giving the dependent a copy of your approved petition which they submit as evidence/proof for their visa application interviews (that is if you didn't include them in your own petition).
These visa classifications include but are not limited to:
Persons with H-1B visas (for specialty workers and their spouses and minor children with H-4 visas), K visas (for fiancees or foreign spouses of US citizens and their minor children), L visas (for corporate transferees & their spouses and minor children), and V visas (spouses and minor children of lawful permanent residents), O visas (for workers who have extraordinary ability and their spouses and minor children), P visas (for athletes, artists or entertainers and their spouses and minor children), and E visas (for treaty traders or treaty investors and their spouses and minor children)
Typically all these are visas which allow you to stay and work in the USA for extended periods of time, not just ordinary visit.