Well, you would think it should be as straightforward as the US embassy website suggests it is, but the truth is that under the new online visa appointment system they advertise, there never seems to be an open visa appointment spot for the next 12 months. The embassy seems to release only a few of these per month. I have been checking their website for a visa for my Mom, for the last 3 months (24/7) along with my siblings from 3 time zones, but every time, we hit a brick wall.
Now we were told by a friend of ours in Lagos, Nigeria, that you may only secure a visa appointment after paying undisclosed sums of money to middle men, who work unofficially or perhaps not, or on behalf of the embassy. Very sad indeed, but does seem to support the well known fact, that bribery is the way to obtain anything in Nigeria. Its unfortunate that the foreign embassies are caught in the same web.