what causes it

Lightning is an electrical charge and it build up in some clouds. It all begins with the smash of ice which are frozen rain drops in the sky. And this makes an electrical charge so after a while the whole cloud will fill up with a huge elctrical charge. An electrical charge can also be made underneath the clouds it can especially be made with things that stick upin the air for example trees mountains and even people. Sooner or later the charge has to go somewhere and where does it go straight in to the ground and then you will see a burst of light come out of the sky.