How do I get my boyfriend from Nigeria, I am a US citizen, I known him for years and we are planning to get married?

Generally, a U.S. citizen may sponsor a fianc? in a K1 fianc?/fianc?e visa application that would authorize a fianc? to enter the U.S. for the purpose of becoming married within the required time deadline, and then the couple could pursue an adjustment of status application process by which the foreign national spouse could become a Lawful Permanent Resident (get a "Green Card"). Alternatively, the couple could become married abroad, and then go through the "consular processing" steps for the foreign national spouse to be able to enter the U.S. and be a Permanent Resident. There are advantages and disadvantages for each option, and of course each option has many details that determine eligibility. It would be wise for you and your fianc? to consult with an immigration attorney who, after learning all of the relevant information, could advise about immigration eligibilities, options and strategies and could offer legal representation in the often complex application process.