What was Carrie's power?

Carrie has the power of what is called telekinesis. In simple terms, this is the ability to move objects by the power of thought. Carrie demonstrates this power at several points in the book. Marbles start dancing around; a hairbrush rises into the air; Carrie's mother is pinned to the door by flying knives; all Carrie has to do is concentrate her mind and energy on an object and scary things start to happen. Telekinesis is an expression of Carrie's emotional life. The more emotional she gets, the more angry and upset, the stronger her powers become. And at the fateful high school prom, the full range of her telekinetic powers are displayed in frightening detail.
Carrie also has the power of telepathy, the ability to read people's minds. This is an important element in the original story, though not so much in any of the various film adaptations. At the prom, Carrie gets inside the mind of her date, Tommy Ross, who feels her talking to him. Carrie also intimidates her enemies Billy and Chris as they try to run her over. She screams her name inside their heads which forces them to crash and burn, literally.