Exercise bands are amazing tools that promote muscular growth and strength, they work by breaking down muscular tissue with resistance training (resistance bands). In order for your body to develop muscle you need to be constantly breaking down the tissues and rebuilding them with protein.
The main difference with exercise band resistance training from traditional free weight training is that you can train in a without gravity with one exercise tool. Weight training only works in one direction you can only contract a group of muscles in one direct. Resistance exercise band training means you can train any part of the body in any directional movement.