The ArcGIS API provides some basic graphics tools to define how features look on your map. If you are creating your own custom graphics, or modifying some existing ones, this portion of the API tells you how to define their symbols. The API also provides custom renderers, which help you define what symbols are used, based on rules applied by the renderer.
The ArcGIS API uses symbols to define the colors, thicknesses, and other visual features of graphics, independent of their shape. In fact, without a symbol assigned, the graphics would not show up. The API defines three simple symbols to highlight points, line, and polygons. Let's look at the Simple Symbols.
SimpleLineSymbol defines the symbology ...