The Skins were created to search for the Royal Four, and, more importantly, the Granolith that their supporters had hidden from Kivar when he took over Antar. The Skins landed near Copper Summit, Arizona and made it their base of operations. From there, they scattered throughout the world, searching for any sign of the Granolith, the Royal Four, or their shapeshifter guardians. The Skins' search proved largely fruitless, in part because the Royal Four remained in incubation for 40 years.
The search went on so long that it looked like the Skins would need new husks to continue. The Skins left in Copper Summit cultivated them, and prepared for the Harvest, where the new husks would be ready for use.
"They are among you now"
In mid-2000, the Skins finally detected the activation of a message from the Queen Mother of Antar to the Royal Four. The Skins leapt into action, and ultimately succeeded in killing Nasedo. Isabel Evans avenged Nasedo by killing Vanessa Whitaker, and learned from her of the Granolith's importance and her original name: Vilandra.
Hoping to learn more of their enemies, the Royal Four and their friends traveled to Copper Summit to attend Whitaker's funeral. Unbeknownst to them, the funeral was a cover for the Harvest. The group narrowly escaped, and was also able to destroy the husks.
Now desperate, the Skins descended upon Roswell in the hopes of finding the Granolith and returning to Antar, since they now had only had months, if not mere weeks, to live.
The Skins were successful in messing with the space-time continuum within Roswell and causing the populace to vanish, but they still couldn't find the Granolith. They were ultimately destroyed by Tess Harding, who unleashed depths of her powers she hadn't known existed.
Nicholas, the leader of the Skins, appeared to have somehow survived, turning up months later in New York. He represented Kivar's interests at the Five Worlds summit there, but was ultimately unsuccessful in furthering his master's agenda. His fate thereafter is known.
Most Skins were loyal to Kivar, and their primary goal was to return the Granolith, a source of great religious (and actual) power to him. The overall fate of the Royal Four appeared to be a secondary concern to them, although there was discussion of returning Vilandra to Kivar.
A minority of Skins, possibly reflecting a political fringe faction on Antar, were as disillusioned with Kivar's rule as they had been with King Zan's. This faction believed that things would have gone differently if Rath had been on the throne of Antar instead of Zan. Their goal was thus to return Michael Guerin to Antar to hopefully seize the throne with the Granolith's power. It's not clear how many of them were left by the time the Royal Four were rediscovered.
The Skins were powerful beings capable of doing many things. Only a few abilities were displayed on the show. Congrasswoman Whitaker was seen using telekinesis on both Isabel and Tess knocking them a couple feet backwords and telekinetically unlocking the door they were behind, which was accompanied by a yellowish light, similar to that of Nasedo's whitish-blue light when he shapeshifts. She also displayed a degree of enhanced strength seen when she ripped an electrical wire from a conductor to threaten Isabel and Tess. When the Royal Four went to the skin populated town they also displayed abilities. A few of them displayed the ability to fire energy blasts from there hands towards Max's shield. Nicholas also briefly displayed the ability to cause Tess, Isabel and Michael extreme mental pain in order to interrogate max.