Easing makes motion feel natural by controlling how speed ramps in and out. Without it, animations feel robotic. With it, they feel alive.
Steps to use easing for smooth animation
Select your keyframes, then right-click and choose Keyframe Assistant → Easy Ease, or just press F9. That’s the quick fix for most animations.

Open the Graph Editor and pull the bezier handles on your keyframes for custom ease curves that match exactly what you want.

Preview your animation — it now flows like real-world motion instead of mechanical timing.
One more thing
Learn the shortcuts. F9 = Easy Ease, Shift+F9 = Ease In, Ctrl+Shift+F9 (Windows) / Command+Shift+F9 (Mac) = Ease Out. If you ever want to remove easing and go back to linear, Ctrl+Click (Windows) / Command+Click (Mac) on the keyframe.
Related how-tos
How to add keyframes in After Effects
How to use the graph editor in After Effects
How to fade in and fade out layers in After Effects
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