The Weeping Angels appeared in “Blink”, Series 3 Episode 10, where Sally Sparrow encountered the Weeping Angels and The Doctor talks to Sally through being a DVD Easter egg. When under observation, The Weeping Angels turn to stone (Quantum Lock) so they can’t be killed, after all no one can kill a stone.
They hide, covering there eyes, so they don’t see each other which makes them look like they are “Weeping”. When touched by a Weeping Angel you are took back in time. The Weeping Angels are incredibly fast and can move vast distances in a blink of an eye. Blink when near one, and your most probably going to be sent back in time.
The Doctor describes the Weeping Angel’s as “The Lonely Assassins”. With a vicious face and sharp teeth, they easily scare those unfortunate to stare one in the eye. (Picture can be seen below)
Feeding off potential energy, keep the Weeping Angels alive. The Potential energy of the lives their victims would have lived in the present. At the end of “Blink” the four Weeping Angels are standing in a circle, staring at each other, being observed therefore quantum locked and never to move again.