The Elders, also known as the Council of Elders or The Founders, were a council of powerful whitelighters who advised magical beings and also commanded the majority of whitelighters themselves.
Approximately 1000 BC, the Elders saw the Titans as a risk to the world and themselves. So they unleashed the powers of the Greek gods onto mortals, who were then able to use that power to imprison the Titans for millennia. ("Oh My Goddess! Part 1")
Their powers are: Invisibility, copying powers, electrokinesis, telekenesis, remote orbing, orbing, thought projection, memory manipulation, healing, glamouring, hovering, light manipulation, clairvoyance.
Despite the fact that many Elders are former whitelighters (as a result of a form of promotion), many are witches or other magical beings who have become Elders due to their services for good. An example of this is seen in Witches In Tights, where Kevin, a young witch, becomes an Elder after the death of Ramus who was killed earlier on and passed his powers on to the youth.
Although believed that the Elders' powers are mental and not physical, many Elders possess powers like electrokinesis. They can also copy powers such as energyballs, but they don't have any effect as they don't actually posses it. Whitelighters can do this too like Nathalie did in Blinded by the Whitelighter while training with the Charmed Ones