I am trying to bring my boyfriend to the USA from Nigeria what do I have to do

So, if you want to get married to your boyfriend and you are a US citizen, then you can sponsor him for a fiancée visa, provided that you have physically met within the last two years. If you just want him to visit, then he has to apply at the US consulate for his own visitor visa. You cannot assist him in anyway with that process. Keep in mind that there may be right now a ban on Nigerian nationals from entering the United States. But that is in flux and it changes on a month-to-month basis