How is magnesium useful? PLEASE HELP!?

I am writing a persuasive essay on how the element magnesium is useful and important to the world. What are flares? It says that magnesium is used in flares, pyrotechnics and incendiary bombs. What are those things? How are they useful whoch makes magnesium useful? Also, what are magnesium alloys used in? (For exp. magnesium-aluminum alloys are used in rockets, missiles, aircraft, etc.) How is magnesium essential to the human body? How do we recieve magnesium if it is needed in our bodies? Is magnesium harmful when burned and how? THANKS!