In storm clouds, tiny particles in the cloud move around picking up positive or negative energy charges, like when shoes scuff a rug. The positive charged particles stay light, and rise to the top of the cloud. The negative charged particles get heavier, and collect at the bottom of the cloud. 

As more particles become charged, they divide into opposing groups in the cloud. When the power of attraction between them gets too great, the particles discharge their energy at each other, completing a path for electricity to travel through the air. We call this flow of electricity lightning. 

It's the negative charges in the bottom of the cloud that cause lightning to strike the ground. When the negatively charged particles group together, they begin to seek out positive charges from the ground below. The excess electrons create a channel of charged air called a leader that reaches down to the ground below. The leaders attract other charged ground-based channels called streamers. 

When the stepped leader from the cloud meets a returning streamer from the ground, the path is ready. An electrical current called the return stroke, travels back up the path. This return stroke releases tremendous energy, bright light and thunder.

The typical stroke can last only 30 milliseconds, so four to five strokes may happen in the blink of an eye. Despite the old saying, lightning does strike the same place twice. 

To review, lightning is created by the attraction between opposite charges, the same force that creates static electricity. But lightning uses huge opposite charges to produce an electrical current that's nothing like what you'd get from static electricity.