1. First, cut out the person you want to apply the effect to. (See the previous tutorial.)
Feel free to add a background layer at this point, but DO NOT merge the two layers. (Personally, I like to have a black layer underneath because it makes the glow more obvious to the eye, and this is what my screen shot would look like at this point.)
2. Select the layer you want to work on (ie: not the background layer!) You want just your person to be the active selection, not the whole layer. Do this by right clicking on the layer and clicking once on "Alpha to Selection". Marching ants should immediately start crawling around the person, not the window - showing your selection is active.
3. Now that your person is selected, Go to the Select menu at the top of the window, and click Select-->Shrink. (For this image, I chose 2 pixels. Fiddle and work out what is best for your image.)
4. Now click Select-->Feather. I used 15 pixels.
5. Select-->Invert the image. This means that the person is no longer selected, but the feathered space around them is. This is a very important step!
6. Now choose your "Foreground Colour". This will be the colour of your glow. For this example, I used a shade of blue (HTML 00c4fd). You may prefer a warmer orange or yellow, or a freaky acidic green. Go nuts.
7. Go to the Edit menu, and click Edit-->Fill with FG colour. (Don't use the bucket tool, whatever you do! It gives a completely different result!)
8. Click Edit-->Cut. Then click Select-->None to get rid of your marching ants. You're done.
9. Try different colours and sizes of glow, and different backgrounds.