If I am a US citizen and I want to bring my boyfriend here from Jamaica and then we want to get married, what steps do I need to do?

Have you met him in person in the past 2 years? If so, you may be able to file for a fiance visa for him.

Generally, the options for a U.S. citizen to sponsor for immigration a fiance who is located outside of the U.S. are: (1) apply for a fiance visa that would allow your fiance to enter the U.S. for the purpose of becoming married within the required time, and then apply for adjustment of status to become a Lawful Permanent Resident (to get a "Green Card"); or (2) get married abroad and then proceed with consular processing so that your then-spouse could become a Permanent Resident. Of course, there are many other details that determine eligibilities. It would be wise for you and your fiance to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies to attain your goals, and who then could offer legal representation in the often complex application process.