Animate strokes to outline drawings, reveal logos, or create any effect where you want something to draw on screen over time.
Steps to animate strokes
Select your shape layer. Go to Add → Trim Paths.

Open Trim Paths and keyframe End from 0% to 100%.

The stroke will draw on smoothly from start to finish.

One more thing
Animate Start and End together for traveling lines that animate across your shape instead of just drawing it in place.
Related how-tos
How to use trim paths on shapes in After Effects
How to add strokes to a shape in After Effects
How to fill shapes with color in After Effects
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