if my fiancee and i want to be married but he's from Nigeria can we

You have two potential options. The first is to petition for a fiancé visa. If the petition is approved, your fiancé can apply for a fiancé visa. This visa will allow him to enter the United States for the purpose of marrying you and seeking permanent residence. You will need to meet certain criteria to be eligible including having met in person during the past two years. The process will take about 6 to 12 months for him to obtain the visa. You will have 90 days to marry after which he filed a green card application.  The other option is to marry. Once married you can file an immigrant visa petition on his behalf. When he enters the United States he will be a lawful permanent resident. This process rakes approximately 12 to 18 months.  You can read more about family immigration at http://myattorneyusa.com/family-immigration.