There are hundreds of ways to do this but here's a relatively simple one.
Firstly you need to learn to use Layers - this way any changes you make can be amended at any time.
1 Open the Layers pallet from Windows. Your photo will appear in this entitled 'Background'. Press Control J - this creates a copy of the original which can be softened and blended in.
2 With the background copy selected (targeted) go to the Filters menu and select Gaussin Blur and enter a radius of between 2 and 8 to blur the whole photo. This should look over-the top... Now in the layers menu reduce the opacity to about 50% or whatever makes the skin tones look soft.... Don't worry that everything else looks soft at this stage.
3 Now select the eraser tool with a soft brush and paint over the areas such as the eyes, teeth etc you wish to keep sharp. This allows your original photo (The background) to come through.
The last stage is better done using layer masks but that would take a little longer to explain.
Hope this makes sense.