Organza and tulle are sheer fabrics but are not the same. Organza is a little crisp and has a smoother and stiffer finish. Tulle is a net like and has a lot of flexibility. Orgaza is used for gowns, structured outfits, and sarees. Tulle is used for layered skirts and veils, also it is great for tutus.
Organza is a lot more elegant and glossy compared to tulle. Tulle is great for more airy appearance while organza is great for a more glossy appearance.