The Narn homeworld has been seen in the episode "The Long Twilight Struggle". It has taken signifigant environmental damage due to the Centauri occupation, and then the massive Narn military build-up which followed the successful rebellion of the Narn slave population.
Among the largest Narn cities is G'kamizad, former home of Narn ambassador G'Kar.
The Narn are a militant people. This was not the case until the Centauri occupation. Before they were conquered by the Centauri the Narn were agrarian, and peaceful.
Their species has both reptilian and marsupialoid traits. The Narn government and social power structure seems to be extremely hierarchical, with challenge by force allowed.
During the Earth-Minbari War, the Narn sold weapons to the Earth Alliance.
The Narn technological level seems to be on a par with that of the Earth Alliance. It is not known if the Narn employ any artificial gravity, or non-Newtonian drives.
The Narn ambassador to Babylon 5 is G'Kar.