Explain the process on how the conditions for lightning to strike occurs?

"A cloud-to-ground lightning strike starts as a channel of negative charges makes its path towards the ground. This occurrence is known as a stepped leader. The stepped leader continues towards the ground in a series of steps that are each about 50 to 100 metres in length. This stepped leader can branch out in many directions. A lightning strike refers to as a lightning flash, is usually made up of more than one stroke of lightning. After the initial strongest stroke, subsequent weaker strokes can follow which usually (but not always) follow the same path of the initial stroke."