I will answer the question that was asked, although I suspect that the real question might be "what is the fastest way to get a visa that ultimately makes me eligible to become a U.S. citizen?"
In general, the way that one becomes a naturalized citizen is by first obtaining a visa that allows permanent residence in the United States by any of multiple available methods, then spending at least five years in that status, and then making an application for U.S. citizenship, which is granted as a matter of course if you pass a citizenship test, an English language fluency test, and a moderately thorough background check.
This five year waiting period is reduced to three years for someone who has a permanent resident visa because he or she is the spouse of a U.S. citizen (incidentally, being the spouse of a U.S. citizen is also one of the fastest ways to get a permanent resident visa).
Special rules also exist to grant citizenship, in the case of people who are seeking U.S. citizenship based upon honorable service in the United States military and sometimes their families as well, and in the case of minor children of people who become naturalized citizens of the United States. I suspect that neither of these options are viable ones in the circumstances discussed in the question.
See generally here.