Thunderstorms are storms with lightning and thunder that form from moisture, unstable air, and lift. They consist of big black clouds that produce lightning and thunder. Thunderstorms can be dangerous, killing 75-100 people annually in the US through fires or direct strikes. Safety tips include staying indoors away from windows or isolated objects like trees, taking shelter in a building or low-lying area if outside, and waiting at least 30 minutes after the last lightning or thunder to resume activities.