There's quite a few ways to do this. Here's one of them!

s t e p - o n e :

Open Pixlr. Choose whatever your background is going to be. Then layer on your person. For this method, you're going to need to have a person that's cut out - whether it be manually or a transparent/PNG. If you want a white glow, make your background darker so it'll easily show up.

s t e p - t w o :

Right click on the person layer and press "Duplicate layer".

s t e p - t h r e e :

It should say that it's a copy. Find that layer and drag it so that it is below the original layer.

s t e p - f o u r :

Make sure you are still on the layer copy. Go up to "Adjustment" and click on "Brightness & Contrast..."

s t e p - f i v e :

Drag the Contrast button all the way to the left. The number should be -100. Press OK.

s t e p - s i x :

Go up to "Edit" and press "Free transform..."

s t e p - s e v e n :

Hold down SHIFT and drag any corner out to the side. You should start to see the layer behind it. Drag it out far enough to see it, but not too far. When it's good, click outside the picture and press "Yes" when the popup appears.

s t e p - e i g h t :

Next, click on the Color Selecting tool. It should be at the very bottom of your toolbar. Select whatever color you want - this will be the color of the glow.

s t e p - n i n e :

Click the Paint Bucket tool. Change the tolerance to about 102. This should cover the whole grey area. If not, make the tolerance higher until it fills the whole thing.

s t e p - t e n :

Go up to "Filter" and press "Gaussian Blur..." I set mine to 50. The higher the number, the softer the glow will be. Press OK.

s t e p - e l e v e n :

If there's some harsh lines on the side of the glow (like in mine), go to the eraser tool. Select a soft brush and erase around the edges. If this messes up the glow, press "Filter" and "Gaussian Blur..." for a second time. Set the amount a little lower this time.

That should do it!