I'm trying to get my boyfriend from Nigeria to Ga, for visit or maybe possibly married how do we start our process and how much are the fees to start

If you are a US citizen, you can sponsor him, as his immediate relative,  to get his green card. There are 2 pathways. He can apply for a K1 Fiance visa, and when that becomes available (takes about 10 months), he can enter the USA and must marry you within 90 days; or after marriage, he can apply at the consulate for his green card (that also takes about a year). Discuss your case privately with counsel about fees and costs. Counsel anywhere in the USA can assist, taking on the case from begining to end.