When animating the position of a layer, we set keyframes. That layer will then move from point A to point B. A simply animation.
By default, keyframes are linear. This means that any animation starts right away and stops immediately when it reaches the last keyframes. For some application this is fine, but most of the time you want to smoothen your keyframes.
A smooth keyframe means that it slowly accelerates when it starts and also slowly comes to a spot. See it as a car that needs to accelerate and break to come to a stop.
This makes your animation natural and smooth!
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