Carbohydrates by definition turn to glucose once they enter the body. This glucose is stored in body tissue as glycogen, which is the primary source of energy for your body. Of course this is an oversimplification, but hopefully you get the picture.
Basically, your body has a number of ways of getting the energy it needs but it prefers certain sources over others. If you have glycogen in your muscles, then that will be the main source of energy. Once that glycogen is depleted it can be replenished if there is more glucose available, or the body can start to metabolize other things like fat and protein (muscle) to use for energy.
Glycogen being depleted in the muscles is the main reason that carbs are consumed during longer duration physical activities such as a football game or running a marathon. Carbohydrates are also the easiest macro for the body to process into energy, and the simpler the carbs the easier it is to digest and use for energy. This is why marathon runners use gel packs that are essentially sugar paste. The easier it is to digest, the quicker it can be used for energy.
Current PRs at 242- 495, 345, 585, 1425