Were do I get the paperwork for my boyfriend to come visit me in the USA and we plan to marry someday .and do it cost to do the paperwork if so how

Yes, you can sponsor him. If you apply for a finace visa, then you must have met your fiance within the last two years. Alernatively, you can travel to Nigeria and marry him there, but he will have to process at the consulate there. The processing times for both pathways is about 1 year, with the Fiance visa taking slightly less time. Counsel anywhere in the United States can represent you. Most of us gove free consultations. Call to discuss. Now, if your fiance travels to the USA on a visitor visa, and you get married in 3 months, then you can adjust status, but be aware that he must enter the country for the purpose of visitation ONLY, and then decide to get married after 3 months. If thats the case, then this is another pathway to consider. Call to discuss.