clouds because of friction of molecluoles biuld up a voltage charge and just sits there charged like a big capacitor waiting to find a path of less resistance to breakdown. the path can be any where another cloud earth any point that it can discharge the potential. when that happens because of the massive charge miles of cloud it discharges with millions of amperes for a very short duration. that generated heat sand can become glass or burn a hole in a tree. or if you lucky and wet it can pass on your dirty clothes and dissipate to ground.