Just do your research. They're not really difficult to keep, but they are pretty specialized fish.
In brief, they'll appreciate a large, well- planted tank, with caves and hiding places, and peaceful tankmates. Expect to feed live food (they love worms) at first. They usually transition to frozen pretty easily, and many will eventually take pellets or even flake.
In the meantime, google is your friend! Check out seriouslyfish and other similar sites. There's tons of info out there, too much to summarize here. Good luck if you decide to go ahead with the purchase...mormyrids are some of my favorite fish!