I am wanting to take the soul trap spell "soul snare" from the mod http://skyrim.nexusmods.com/mods/8971 and add the chain magic effect to it. I was playing around with the spell in the creation kit and I couldn't figure out what the chain effect was. I really have no experience modding but have watched some of the tutorials and one specifically about creating spells but it didn't cover that specific effect. Can anyone offer any input on how to do this? Thanks.

Look at the explosion for chain lightning. Alternatively, findclosestactor is great for chain effects.