Cannabidiol, or CBD for short, is an organically derived molecule, most commonly found in the Hemp plant (but is also naturally present in the female Cannabis as well). The reason CBD is so beneficial is because within our bodies, we each have an Endocannabinoid System that responds to CBD, telling it what the body needs to thrive.
Ultimately, CBD (and other cannabinoids) works to balance immunological, physiological, and psychological processes. Homeostasis is the goal. Cannabinoid receptors are located all throughout the body, including the brain, the central nervous system and the peripheral nervous system (digestive tract, immune system, skin cells, heart, etc.) which is why research suggests cannabinoids provide such general health benefits.