There are two primary sources of citizenship: birthright citizenship, in which a person is presumed to be a citizen if he or she was born within the territorial limits of the United States, or--providing certain other requirements are met--born abroad to a U.S. citizen parent, and naturalization, a process in which an immigrant applies for citizenship and is accepted. These two pathways to citizenship are specified in the Citizenship Clause of the Constitution's 1868 Fourteenth Amendment which reads:

is naturalization the same as becoming a citizen?
yes