Superposition

Here are two waves that have amplitudes of 1.0 travelling in opposite directions:

Stationary/Standing Waves

When two similar waves travel in opposite directions they can superpose to form a standing (or stationary) wave. Here is the experimental set up of how we can form a standing wave on a string. The vibration generator sends waves down the string at a certain frequency, they reach the end of the string and reflect back at the same frequency. On their way back the two waves travelling in opposite direction superpose to form a standing wave made up of nodes and antinodes.

Nodes          

Positions on a standing wave which do not vibrate. The waves combine to give zero displacement

Antinodes 

Positions on a standing wave where there is a maximum displacement.