Apply an effect and transform what your layer looks like — effects are the core of After Effects.
Steps to apply an effect
Select your layer and go to Effect → [Category] → [Effect].

The Effect Controls panel opens where you can adjust all the settings for that effect.

Preview your comp and tweak the effect settings until you’re happy with how it looks.

One more thing
If you’re applying the same effect to multiple layers, select them all first and then add the effect — After Effects applies it to every selected layer at once. Saves time instead of adding it one by one.
Related how-tos
How to add a shadow in After Effects
How to search for effects quickly in After Effects
How to add glow effect in After Effects
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