What is an animatic ?
The animatic is the next step after a storyboard. An animatic is just an animated and rhythmic storyboard that will be used as a reference for animators.
Traditionally, it's very long to turn a paper storyboard into a video (you have to scan, cut, edit...), but with TVPaint Animation, this step is instantaneous.
As each clip is composed of one layer and one image at least, you just have to give a duration to each image to create your animatic.