Hello im folloing a tutorial and there is a step like this
"TIP: Iíve placed many cliffs/rock near
my coasts, but I didnít want the rocky
color in the water, so I select the base
land layer & chose the land itself, then
switch to the rock layer. This prevents
the pen from marking anywhere outside
the land."

Im not being able to do that. So i want to paint something in a layer but i want it to fill only the space that is alredy filled by a pre-determined layer. The 2 layers are not adjascent.