Four kinds of band, four different jobs. Every exercise on this site names which one it needs.
A short, wide loop, usually fabric. It sits around your thighs or ankles and pushes your knees together, so your glutes work to push them apart.
Where it goes: Above the knees, around the ankles or around the feet.
A round rubber tube with a handle at each end. You stand on it or clip it to a door anchor, then pull the handles like a cable machine.
Where it goes: Under your feet, around your feet or clipped to a door anchor.
A long, flat loop of layered latex. Strong enough to load big moves like deadlifts, squats and push-ups.
Where it goes: Under your feet and over your back, or across your back and under your hands.
A long, thin, flat strip with open ends. Light resistance for shoulders, warm-ups and rehab-style work.
Where it goes: Held in both hands, or wrapped around your hands for grip.