MultiBarRightButton1 - This refers to the further right, of the two vertical bars, in the default wow interface. If you press Escape, then click Interface, then Action Bars, click the options to make all your bars visible.

Button 1 - This is the first button, and counting downwards, the last button is Button12.

The Castsequence for Flame Shock, needs to be put on Button1.
And then LvB on Button2, C.Lightning on Button3, and L.Bolt on Button4.