Pop of Color Photoshop

Question

I want to have the background be black and white and then a rectangle of color be normal but I don’t know how and when I erase it it’s shaky. What do I do.

Answer 1

Add a black and white adjustment layer to a colour image, select the layer mask in the layers panel, make a selection using the Rectangle Select tool, and then do Edit > Fill, and choose black as the fill colour.