Bones, muscle, and skin work together in the human body by providing the body with structure and organs with protection, by moving the body and allowing organs to function, and by containing and protecting all bodily materials, respectively. Bones and muscles (referred to as the musculoskeletal system) work in tandem to perform most physical functions, while skin (the largest organ in the body) protects this and other systems.
Bones' primary function is to provide structure and shape for the human body. The 206 bones in the skeleton also cover and protect some of the most important organs, such as the heart (covered by the ribcage) and the brain (covered by the skull). Though bones determine the shape of our limbs, muscles are needed to create movement.
Muscles are connected to bones by tendons, and use this physical proximity to move the skeletal system. Muscles contract and expand along the bones they are attached to, creating a range of motion. The type of muscle most intimately connected with bones is skeletal muscle (in contrast to smooth muscle which lines organs, and cardiac muscle in the heart).
Skin is the organ that contains bones and muscles and protects them from the outside environment. By regulating temperature, pressure, and what is absorbed into the body, skin creates a context in which other bodily systems can function.