A futanari is a Japanese term (obviously), that means that you have both sets of genitals (futa means 'two'), much like a hermaphrodite, except that they typically have overly large genitals, unlike their real world counterparts, and they are fully functional. In the fantasy, they typically hypersexed, and many have proclivities toward exhibitionism. Testicles are optional, as are breasts, some have them, some do not, but they must have both a penis and vagina. They generally consider themselves women, but occasionally are made to use the men's changing facilities in the fantasy worlds in which they are more common. They are also natural (or magical in some cases), not typically surgically created.
If you have breasts and a penis, but no vagina, then you are not a futa, that would be something else, depending on how they came to be that way...