Timing is how fast or slow somthing is moving in an animation. A object with very fast timing will move very fast when the animation is played. A car has very fast timing. Timing is very importaint when animating because it is what humans are acostomed to seeing. We know the timing of how fast or slow people talk. We know the timing of how fast a airliner should be flying. If a plane in a animation is moving very slow, then the animation will feel unatural.
Timing will make you animations feel natural. However this is not the only
thing that will make your animations feel natural. Timing is just one
of the priciples of animation. There a twelve of them. I find that timing
is a really impotaint one. It works with many other pricibles, but you cannnot
use most the other pricibles without good timing.
Spacing litterly depends
on timing. If you make a slow object move fast, then it will be spaced
akwardly on the screen. Easing requires that you can make things move fast
and/or slow. Timing is very importaint.
So how do you accually apply timing? On the basic level:
If I want to make a ball move across the screen very slowly, then I would add many frames of it moving. The more frames, the slower the ball moves. This is all because if you have 24 frames of the ball moving accross the screen, then it will take one second of animation to play those 24 frames. But if you double that and make 48 frames of the ball, then it will take 2 seconds to move. The opposite also works. Having less frames of the ball moving will make it move faster because it takes less time to show less frames.