Did you ever have the deck of cards which when flipped showed an object moving?

Then you understand that animation is just a (large!) sequence of still pictures. It takes 24 frames to make 1 second of reasonable animation.

Like a movie, animation is just a series of still images played in sequence.

While Disney Studio used to draw such pictures by hand, now a computer process called "in-betweening" is used.

First the image, say, a ball is drawn. Then for the movement, a future position and possibly a path is indicated. Computer software then calculates and creates the in-between frames.

Macromedia Director is a multimedia presentation package which performs in-betweening to produce animation.

Animation can be:

Two-Dimensional

Three-Dimensional

Morphing

Server Push/Client Pull Animation for the Web