I have a pen. / I have got a pen. Formal U.S. English: What do you have? I have a pen. Informal U.S. English: I've GOT a pen right here for you. ("Got" is used for emphasis, since it's unnecessary in U.S. English.) One of the ways I can tell if a student has been studying British English is when he/she asks me, "HAVE you GOT a pen?" It sounds strange to me, since I know he/she is generally not familiar with casual English. I understand the question, but that's not how an American would formally ask it. Informally, maybe.

"Mary has got a boyfriend" and "Has Mary got a boyfriend?" are not correct but are commonly said colloquially. Many Americans would correct each other about such a grammar mistake though. When still learning English, always say "Mary has a boyfriend" and "Does Mary have a boyfriend?"