This tutorial is for adding a focus element on a photo that lacks one. For example, in my example image, the main element is not distinguished clearly by the viewer because of the heavy background. Also the background is in the same tonality with the subject and this doesn't help the girl.
Now our main task is to make a difference between the girl and the background. There are many ways of cutting an image. I've chosen Extract. So duplicate the layer and go to Filter > Extract.
Choose the pen tool and begin drawing the subject like in my example. After you're done, take the paint bucklet in the same extract window and paint the girl to show that you want that area kept.
When you are satisfied with the selection, hit OK. If you click to turn off the main layer visibility, your image should look like this:
Turn the layer visibility back to ON and hit CTRL+U to bring the HUE/Saturation dialogue up. We have 2 choices: to make the background grayscale, so we would drag the slider of the saturation down to -100% or to change the background tones. In my case, I used the second variant.
This is the new photo and you can clearly see that now the main point of the photo, that attract the viewer from the very beginning is the girl.
