What is the process I must follow to marry a foreigner?

I am a US citizen and I reside in the US. My problem is I am in love with a Nigerian man that reside in Nigeria and has never came to the US or has ever applied to come to the US. I someday would like to marry him and we both reside in the US together. Can anyone tell me the complete process I and he is to follow to make this happen? I would also like to know how long the process takes and what all will be required of me.