Drakh physiology is unclear. Some Drakh appear to be "blurred", indicating that they exist in some unusual physical state, but this characteristic was only observed once, so there might have been some kind of technology in use.
Drakh are humanoids with greenish skin. Some drakh appear to have white, skull-like faces with glowing red eyes, but this may be a helmet of some kind.
Some Drakh are able to produce parasitic creatures known as keepers that can attach themselves to other humanoids to control their actions.
Virtually nothing is known about drakh organization. They were subservient to the Shadows, but how they govern themselves is unknown.
The Drakh apparently served as a working caste on the Shadow homeworld, Zha'Ha'Dum, helping to maintain Shadow facilities and performing other tasks in return for advanced technology. They played little role in the Shadow War, but when the war ended and the Shadows left the galaxy, they remained on Zha'Ha'Dum until the self-destruct device was triggered, destroying the planet.
The Drakh wandered for a period of time in search of a new place to settle. They attempted to negotiate a deal with the Minbari, but when they found out they were dealing with Delenn, they attempted to kill her. They subsequently managed to infiltrate Centauri Prime placing keepers in key officials of the Centauri government to secure control. The Drakh presence on Centauri Prime was eventually defeated under unclear circumstances.
The Drakh are few in number, but they do possess a fleet of advanced warships and some Shadow technology. They appear to be able to rival the technology of the Minbari. They were capable of threatening Earth with their own forces (attempting to deploy a salvaged Shadow planet killer and successfully deploying a techno-organic plague), although it's seems unlikely they would be able to sustain a prolonged war effort.