A Drop Shadow effect adds depth and separation so your text or graphics don’t blend flat into the background.
Steps to add a shadow
Select your layer and go to Effect → Perspective → Drop Shadow.

Adjust Distance and Direction to place it where you want it, then tweak Softness and Opacity to taste.

One more thing
Duplicate the effect and use a lighter opacity plus larger softness for a subtle ambient outline sitting behind the main one. Creates dimension without looking fake.
Related how-tos
How to add stroke around text in After Effects
How to make glowing text in After Effects
How to create a blur effect in After Effects
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