Complex sentence: Best Buddies International is a nonprofit 501 (c) (3) organization which has established a global volunteer movement that creates opportunities for one-to-one contact, integrated employment and leadership development for people with intellectual and developmental disabilities (IDD).
Split into simpler sentences: Best Buddies International is a nonprofit 501 (c) (3) organization. It is comprised of volunteers that that attempts to create opportunities for people with intellectual and developmental disabilities (IDD).