Glow/Bloom effect is a pretty easy effect to implement (compared to some of the other effects out there) and is usually done in 3 steps.
1. Render your game scene into a glow map texture/fbo, only the parts that are to glow should be visible on this, the rest of the scene is usually not drawn or blacked out where it partly covers any bits that need to glow.
2. Blur the glow map, usually using something like a Gaussian blur.
3. Blend the glow map texture on top of your game scene (normally using additive blending).
As for actual implementation there are a number of tutorials available online showing how to do the above.