"The story is king. The story is king" is a famous mantra of Pixar. You cannot have a good animation without a good story. The story comes first.
When we storyboard we start with the "keyframes". The keyframes are the key moments in the scene. It is like outlining a story. The Keyframes are the chapter headings. I tell students to sketch out the keyframes first. Then they create the "tween" frames. The frames that get you to the next keyframe. There is a one to one correspondence from drawing to camera still images. In other words, each box represents a click of the camera.
After your storyboard is complete, it is time to write the script. The script can be written on lined paper or on the back side of the storyboard.