Below are two plots relating to the same wave.
The upper plot shows the actual shape of the string. The horizontal axis is x while the vertical axis is y . The wavelength is the distance, for example, between one peak and the next.
In the second view see the motion of the single blue particle, plotting y as a function of time. In this plot the distance between two peaks is the period of the wave, the time that the blue particle takes to make a full oscillation up and down.
Modified from Andrew Duffy's web page at Boston University. The animation uses the Physlet Java Applets of Wolfgang Christian and Mario Belloni.