Muscles move our joints by pulling on tendons, which then pull on bones resulting in action: arm bend, knee lift. Many muscles work in pairs (synergy).
The brain sends a message via nerves to the muscles. One muscle then contracts becoming shorter and fatter (thus pulling the tendon and bone towards it) while the other muscle relaxes.
Muscles work in pairs, as one contracts the other relaxes..
Muscles pull, they cannot push.
Cartilage covers the ends of bones and allows smooth movement at joints.
Diagram of Knee Buckle-handle tear of cartilage
Both images from Wikipedia
