The legend displays the series in a chart with a predefined symbol and the name of the series. The legend can be customized via the Legend class. The most important properties allow you to change the legend position, orientation or aligning:
<Legend RenderDirection="Vertical" Align="Right" VerticalAlign="Top"></Legend>
<Legend RenderDirection="Horizontal" Align="Center" VerticalAlign="Bottom"></Legend>
Also all displayed symbols/names pairs into the legend are selectable. This allows you to show hide dynamically all rendered series into the chart.
Live demo can be found here.