How do I replace the 'alpha maps' + other maps

Hey!

So today I was making a sink for the first time, and while in the Warehouse tab, I found a couple more maps than usual (cloned the Amaranth Sink, which has transparent parts). However, there was a map I hadn't worked with before (it was black and white, I believe it was the alpha map), so I'm just wondering, how do I make a map to replace this map?

if you still don't know what I'm talking about, here's a picture of the map
I'm also wondering what these maps do too, if anyone can tell me, that would be greatly appreciated.

Thanks in advance!