Cordage is the general name for various kinds of twine, string, and rope.
Rope can be made of all kinds of fibers: hemp, sisal, polyproplyene, nylon, to name a few.
String and twine is often made of cotton, but there are synthetic materials used as well.
Every good boyscout knows basic knotwork. Knots are loops of rope folded against themselves to
secure the ends to various things. The square knot is a simple knot to tie two pieces
of cordage together.