First up, Grab a good photo for Experiment on. I found this one good. you may choose it too.
Open photo in Photoshop by pressing Ctrl+O or going to File/Open and Press Create a Duplicate Layer By pressing Ctrl+J or go to Layer/Duplicate Layer Hit The Enter Key.
Lets Open Filter / Blur / Gaussian Blur and change the Radius to 5 (Note – You may change it to accordign to you image resolution)
Now select Elliptical Marquee Tool by by clicking right mice key on Marquee tool
Finally Press Delet key to Remove Blur from the above layer and get Depth of field Effects