The Drej social order seems to consist of two castes: multitudes of Drones, and a small number of ruling class. Whether or not these are the only positions in their society is never explored. Additionally, only two Drej ruling caste are ever seen: The King and Queen. They do not seem to be capable of speaking English but they do have their own language, consisting largely of mechanical rumbling noises and inhuman shrieks.
Upon first inspection, the Drej are not much different from our species. They're not corporeal entities, yet they have a physical form which appears to be both skeletal and humanoid.
All Drej are made entirely out of pure energy, giving them a bright blue glow. At the front of their heads is what appears to be an eyespot, which, according to the novelisation, also houses a mouth, the latter of which is not seen in the film. Despite their physiology, however, they are tangible and can manipulate objects just as easily as other sapient races. Furthermore, when a limb is destroyed they can regenerate it in a matter of seconds, possibly by extracting energy from their surrounding environment. Drej can fire portions of their substance at foes in a concentrated blast, although whether or not this expenditure of energy subsequently weakens their physical form is not explained.
Ships & Technology
Like the Drej themselves, their technology is also made of pure energy. In at least one known instance, non-Drej beings have been able to escape captivity and move through Drej ships by putting two objects (i.e., Hands) against surfaces and then separating them, interrupting the energy flow and allowing passage.
The Drej have two primary modes of transportation. The bulk of their fleet is made up of swarms upon swarms of smaller, aggressive looking ships called Stingers. Making up both the offensive aerial forces, as well as prisoner and cargo transport, the Stingers consist a small central fuselage with pairs of sharp fins on the back and sides, and a pair of long arms extending up and forward from the body, then levelling off, and angling back down, inward toward each other.
The second type of craft is the large mothership, called the 'Alahenena' (supposedly the Drej language term for "Planet Killer"). The craft is incomparably massive in size, and powered by a white dwarf star, eliminating the need for fuel. Not only does the flagship house the Drej population, but is also capable of, as its name would suggest, destroying entire planets, as demonstrated on the Earth. To do this, it positions itself over the planet and fires a beam of kinetic energy at it, causing the planet to spin faster and faster, until its centrifugal force overpowers its gravity, thus causing it to rip apart at the seams.
In the Titan A.E. prequel comics, it is explained that the mothership is part of the reproduction cycle of the Drej. The Queen Drej gestates a new generation by adsorbing the rays of pulverised planets. The absorption takes decades before the Drej then move on to the next world.
Their weapons, referred to as "Focus Burners" in the novel, channel photons into a beam, turning light energy into heat energy, that can even melt through starship hull when concentrated. In addition, the Queen has an advanced computer system, known as the Orb, with which she can see through her Drones' eyes.
In the book, the Drej are seen quite differently. Early in the novel, when Cale sees them on Tau 14, one of them "ha[s] its mouth open, and the interior [is] pitch black". In the film, however, no such mouths are seen. It was also noted that they had some sort of black, fleshy envelope above the pulsing energy, possibly the eyespot seen in the film. In addition, when Cale is captured, they speak using pulses of light instead of rumbling and whirring noises. There also appear to be different types of drones as well: Deeheh, who serve as scouts; Daiheh, who oversee ground transport; Droheh, who can fight, and Douheh who serve as thinkers and strategists, with high level cognitive abilities.
The book also includes chapters from the Drej's perspective. The Drej Queen's name was Susquehana, one year, of the planet the Drej were from was called a Making, because every year the Drej would make more Drej. They could calculate much faster than any human, they had a piece of technology called the Orb which would act like a computer, only much stronger and capable of doing things. The Drej believed that nothing except duty is important. They were not even familiar with the concept of a friend. They suffered no disease, lived for thousands of years, and were not afflicted with a need to procreate. They possibly got more Drej by the Lanoor, a piece of technology capable of making more Drej, but it is unknown how they created more Drej before they had technology. They called their stingers Slijah. The ones specifically shown were Praojeh class.