Animation is a series of images, each slightly different from the last, shown in sequence. When they are shown fast enough, we stop seeing the individual images and instead see an illusion of motion. There are many ways to create the individual images including hand drawings and photographs of objects. Pixar makes their images with virtual 3D models and sets.
Animators bring the story to life, posing characters to act out each scene. They start by breaking down an action into a series of poses called key frames that mark out important positions. Then, they use a computer program to describe how the object moves in between those key frames so that the resulting animation conveys the desired emotions.
Continue to explore using Pixar in a Box, a set of lessons developed by Pixar and Khan Academy. Follow the link for a lesson on Animation.