Layers must be one of the most misnamed things in AutoCAD.
The one thing that AutoCAD “Layers” don’t do is actually layer objects. This is controlled by the Draw Order commands. That’s what I mean when I say “Layers” are not layers. They are nothing at all like the olden-days concept of drafting on transparent paper and layering them on top of each other.
AutoCAD “Layers” should be called Collections, or Bundles. They are a way of grouping objects (lines, blocks, text, whatever you like) together so you may easily adjust properties they share. The most obvious and prolific use is color. When you set the color property all of the objects on a “Layer” to “ByLayer” then you change the color of everything in that “Layer” simply by changing the color of the “Layer”. This is ultra-handy because it centralizes object properties you want to tweak, en masse. If you want to change the color of video cables in a drawing from blue to pink, you only need to change it in one place – on the Video “Layer” in the “Layer” manager.
“Layers” also work inside blocks. Anything inside a block that is not on “Layer” 0 (zero) is a member of the “Layer” it is assigned to and will change along with everything else on that “Layer”. Layer 0 (zero) inside a block is a whole other topic.