If you are having a hard time understanding how the nodes work, then this post where I explain how to recreate photoshop layers with nodes might help you out:
I would do what carl said and invert the black and white texture, then use that as the factor in a mix shader that mixes the main shader for the body with an emission shader. If you don’t want the glow to be uniform across the whole crack, then I’d multiply the inverted cracks texture with a noise texture and use that as the factor for the mix shader.