How do I create respective layers for separate pieces of sculptures?

I’m not sure how to use the layer feature for different sculptures in Blender?
Example:

• #1 Sculpture should be on #1 layer, and same for #2 sculpture on #2 layer… Not this way: #1 and #2 sculptures on a same layer at all.
  I’d like to be able to carve #1 sculpture without causing #2 sculpture to act like it’s being treated the same way.

• Another Example: Supposedly if I want to be able to create asymmetrical tail on a cat’s body, I should be able to do that without it altering the cat’s body at all.

I’m trying to figure out a shortcut, or at least how to get it to work…
I’ve tried ask this question on Blender Discord, and Reddit (which I copy-pasted most of my question into here).

• Then eventually, I got an answer on the discord server that I should try a shortcut command which is Shift + A in the sculpt mode. Which I assume is masking an area (light gray-colored area) on a sculpture to make it only be able to inflate… rest of the sculpture that can’t be inflated is dark gray-colored area…
  — Sam

(#1 Edit: Removed 2nd question; #2 Edit: Thank you for the responses, I appreciate the question you had for me – though I don’t think it’s the answer at all since it’s masking not layers solution.)

• Sam