Layer Adjustments can be a complex area and you may want to experiment with some of them to find out what they do. Briefly, using Layer Adjustments uses Adobe's powerful built in filter technology to decide how layers interact with each other (or rather how a layer affects the layers below it).
Returning to the blurring image, this simple task shows you how to make an image more effective by using a Layer Mode to improve an image . Follow the steps to see how it works:
Open the nodding donkey image on the left (by clicking on the image or the link on the left to open the full resolution version). Remember that it will open up a larger version in a new window. Right click on the larger version and choose 'Save image as' from the drop down menu. Save it in your working images folder or on your USB stick.
When you have downloaded the image, start Photoshop and use FILE > OPEN to locate the image and open it.
Duplicate the image (background layer) by right clicking on the layer in the Layer palette and choosing 'Duplicate Layer' as shown.
Now set the new layer's Mode by using the drop down mode List (arrowed, left) and choose 'Multiply'.
The image should now appear to be more highly 'saturated', improving what was originally a rather 'washed out' or overexposed image.
You may want to adjust the image further using the brightness and contrast controls sparingly.