The skeletal system is composed of bones and joints which provide structure, protect organs, and enable movement. It includes elements like the skull, rib cage, backbone, and limbs. Joints are where two bones meet and are held together by ligaments, allowing movement except in the skull. There are different types of joints like hinge, ball-and-socket, and pivot joints. Muscles connect to bones via tendons and work with the skeletal system to produce movement, with some muscles being voluntary and others involuntary.