Open the image you want to edit on your PC's image editing program. Pay-for programs like Photoshop and Corel Paint Shop Pro are extremely capable, but freeware programs like GIMP (Gnu Image Manipulation Program) also exist online.
Duplicate the background layer first without selecting anything on the screen -- this will ensure you don't duplicate just some of the image or miss any edges. Most good photo editing programs have a shortcut for duplicating a layer. For example, this command is "Ctrl + D" in Adobe Photoshop.
Select the new layer in the layers menu or on-screen box and change the blend mode to an Overlay option. Do this in Photoshop by using the dropdown menu in the layers box and by selecting "Overlay" from the choices available.
Apply a Guassian Blur to the image with your duplicate layer still selected -- this will add the soft focus and glowing effect to the image. Find the Gaussian Blur option in your program's "Filter" or "Effects" menus and alter the strength of the blur by changing its pixel radius value. A pixel radius value of around 8 is a good level for a softer glow, but you may need a higher value for high-resolution images.
Reduce the strength of the effect if the glow is too obvious or strong. Do this by lowering the opacity level of the duplicated layer -- a soft focus will appear less intense at around 60% opacity.