The Weather Book is my favorite quick source on weather-related matters. By comparison, sound dawdles on its way to us. It takes about five seconds for the thunderous sound of a lightning strike to reach a mile away. Properly, the form of rowdy weather that produces this sound and fury should be called a lightning storm rather than a thunderstorm because lightning is what causes thunder. Apparently the real cause of a storm's rumbling is heat.
Most people have a general understanding of lightning basics.
Typically, a negative charge builds up in the cloud and a positive charge builds up on the ground. Electrons, which carry a negative charge, begin zig-zagging downward in an invisible, jagged flow. When they meet an upward-flowing streamer of positive charge, a current begins to flow. That's a very calm way of describing the titanic force of the upward leap of intense positive charge that makes up the lightning stroke we see. Yes, lightning really does strike up.