This simple example adds a small border on the image which is often desirable for prints on your home printer.
 

Fig. 1.  Before - with no border

Fig. 2.  After - with black border

The following steps add a 12 pixel border in black.

• Change the "Background Color" to a color of your choice.  Skip this step if you already have the proper color.
• At the bottom of the toolbar, there are 2 large rectangles.  Click on the lower one to change the background color.
• Either interactively select a color of your choice or type in RGB values.  In this example, I simply typed in 0 (zero) for Red, Green and Blue to obtain Black.
• Click OK.
• Image > Resize > Canvas Size.  See Dialog box in Figure 3.
• Check the Relative box
• Change both measurement types to Pixels (this is easy to forget)
• Enter a number in each of the boxes for Width and Height.  I used 12 in this example. (see note below)
• Click OK.

Fig. 3  Dialog Box for Resize Canvas

Notes:

• I used a 12 pixel border for these small images, whose dimensions are 400 by 348.  For a 2 MP image, a proportional border would be about 40 to 50 pixels.  For a 5 MP image, a border of about 70 would look similar.  Feel free to experiment with larger or smaller borders.  These sizes were given as a starting place.
• In most cases, a neutral border is more effective.  Black, gray, and silver are usually good choices.  White is a good choice if printing on a dark background.
• Photoshop Elements has a few "frames" that you can use, but they are not very good.  Elements also allows you to slightly jazz up a border using Layers and Layer Styles.   JASC PaintShop Pro has a nice selection of frames, and you can get frames from third parties.  However, even nice fancy frames are printed on flat paper, thus they look flat.  I recommend keeping your borders simple so that the viewer focuses on the image, and not on the border.