The easiest way is to simply copy the "base color" map to the "Emission Color" slot and set the emission color to anything other than black ( 0 0 0 ) . This will make most things glow.

You will want to change the "Luminance Units" to something suitable for the surface you are trying to make glow. cd/m^2 is a little on the low power side. kd/m^2 is much stronger. You might need to experiment to find what one is best for what you are wanting to illuminate. Switching to "W" (watts) opens up "luminance Efficancy" which is in lumen per watt.

Turn "two Sided Light" to Off unless you want light emitting from both sides of the surface (not very useful for a button on a console)

There is also an "Emissive" shader that should really be used on the surface you want to make glow. You can also use Emission profiles ( "IES" profiles ) if you want to do something a bit more fancy.

I use the aforementioned "simple" version to make things like computer screens and TVs glow with a picture on them.I'm sure there is a right way to do it, but this way works for me :) here is a render I've been working on that shows what I get when I use this method. It's a bit rough still. I haven't gotten the bodysuit just right yet, but it's getting close to what I want.