Layer order matters — what’s on top shows on top. Rearranging your layer stack is simple once you know how.
Steps to move layers up and down in the order
Select the layer in your timeline.

Press Ctrl+Alt+Up/Down (Windows) / Command+Option+Up/Down (Mac) to nudge the layer up or down in the stack order.

Or just click and drag the layer to a new position in the stack. Either way works — pick whatever feels faster.
One more thing
To jump a layer straight to the very top or very bottom, use Ctrl+Shift+] / Ctrl+Shift+[ (Windows) or Command+Shift+] / Command+Shift+[ (Mac). Way faster than dragging when you need to move something all the way.
Related how-tos
How to duplicate layers in After Effects
How to hide and show layers quickly in After Effects
How to rename layers in After Effects
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