There's excellent threads on the topic over on altered time, but to give you information on what I know - its a build that completely ignores some spells and only uses frostbolt, icicles, and GS. It's heavily mastery dependent and to some extent crit is nice too because if GS doesn't crit its apparently a large loss of damage - which makes sense the difference between 2.5M and 5M dmg GS is big.
Thats the super simple version if you feel like playing mindlessly. The optimal way you use fingers of frost charges at 3 levels of chain reaction but only if RoP is down and also cast frozen orb when RoP is down as well, you also make sure to shatter frost bolts with flurry for the increased icicle damage.