Thunderstorms are born by a seething mass of condensed water vapor. That mass is called a cumulonimbus cloud. This huge cloud can produce strong winds, heavy rain, and even hail.
Lightning in thunderstorms are produced by the friction of the clouds rubbing together, or small bits of ice(frozen raindrops) bumping into each other. At least 100 bolts of lightning hit every second.
Some bolts strike with bizarre shapes. As you can see, in the background there is a loop of lightning that is pink.
Here is a video that explains how strange lightning forms: