Why does Gatorade give you energy?

From sugar. No matter what you're consuming, if you're talking about energy, you're eating something that is sugar or that your body breaks down into sugar (like carbohydrates). Other things are needed by your body for many reasons, and if you don't eat any sugar (such as in "low carb" diets), things change a bit, but for a normal metabolism, it's the sugar in Gatorade that gives you energy.