Your body contains a vast array of muscles which control virtually all of its functions. However, for sports we are primarily concerned with the skeletal muscles which control locomotion. There are hundreds of these, most with bizarre names , but we will usually simplify the discussion and only talk about the major ones. The skeletal muscles attach to the bones via tendons, which are made of strong, rope-like tissue. If you wiggle your fingers and look at the back of your hand you can see the tendons that connect your fingers to muscles in your forearms.
Most muscles end in a single tendon, but there are exceptions.
The biceps muscle ends in two tendons, and the triceps ends in three. Each end of a muscle is attached to a different bone, and the two bones in question will meet at a joint. Like the forces in Newton's 3rd Law, muscles come in pairs. The pairs are arranged opposite one another so that one muscle will open a joint, and the other one closes it. There are many other muscles attached to the elbow joint which serve to stabilize it, etc.