Photoshop Elements :: Creating Transparent Background On A Photo?

I have photoshop elements 7.0 and I am having difficulty making making a photo with a transparent background.  According to the tutorials I watched, I am supposed to bring the desired photo which I do and can be seen on the right in the layers box dialogue.  Then there I create a copy which is "unlocked" which shows up on my screen.  Then, I select the brush tool and I select the areas of the photo which I wish to make transparent and then hit the letter "D" on my keyboard, or the delete button.  Although the background is seen gone in the photo in my layers box, the background is still shown in my photo on my screen.  The perforated lines are seen and although I keep pressing the D button it does not work.