I would like to draw an outline of a chess piece and then color inside of the chess piece only which I know about the alpha lock option. So I want to color only inside of the outline then also make mountains inside of the chess piece but multiple mountains so multiple layers but i'm not sure it's possible to make Layers Inside of Layers.

So basically how can I make layers inside of a layer.

The alpha lock method is very simple way of restricting paint but it's also limiting and constraining for what you seem to want to do.

(You can do it using alpha inheritance inside a group but that's confusing unless you're familiar with the technique.)

I'd suggest that you do the mountains as 'layers inside a layer' by grouping two or three (or however many you need) paint layers (select multiple layers -> rigth-click -> Group -> Quick Group) and then using the chess piece shape (white on a black background) as a transparency mask (right-click -> Convert -> to Transparency Mask) for the group layer. In that way, you'd keep everything separate.

You can construct the chess piece outline and white shape fill separately (using the Fill Tool options) and so have an removable outline then make the transparency layer by merging the chess piece white fill with a black layer underneath it.

Here's a quckly done example and I'm sure you could do a better looking chess piece and better looking mountains.

https://i.imgur.com/R5QCAQX.png