Oh my gosh, that doesn't sound very clear when I read it back this time. I will go into PHotoshop Elements and see if I can make the selection tool part more clear. In the meantime, painting means to grab a soft edged brush and paint with black on the mask to hide or paint with white to reveal. So you paint away the parts of the photo you don't want, if you get too much, switch to white and you can paint some of the photo back.
You can just as easily erase the parts of the photo you do not want, but it you take a little too much, you'll have to undo. With the mask, you have more control. Does that help?