Step 1 Masks can be confusing because you can’t see them, so here’s a demo that will make learning the basics simple. First, duplicate your background layer. Then go to Image > Adjustments > Desaturate. This will take all the color out of your Background copy layer. Now add a mask. To do so, just click on the mask button.
(Desaturate is a terrible command for converting to black- and-white, but it works for the purposes of this workshop)