They are formed from smaller molecules that combine to form chains, like people holding hands to make a chain of people. The molecules tangle like strands of spaghetti, giving special properties. Spandex is a type of polyurethane, a class of polymers which is also used for foam cushions. Polyesters are another class of polymer. Uses of this polymer vary from clothing to plastic pop bottles.
Rayon is made from a natural polymer that is specially treated before making the fabric.