It is easy enough to create a drawing with lines, but that does not make the drawing easy to read. Using colors and graphics will help others to read your drawings. In many cases, making your drawings easier to read will help your clients to understand the drawings, it will help the builders to understand your drawings and details, and it will help local authorities to understand and approve your drawings.
The Attributes Palette is the main way to assign graphics to your objects unless you are using classes to control the graphics. Even then, you have a dialog box that uses similar concepts.
This is how Vectorworks assigns colors to objects.
Applying Line Weight and Line Style.
This is how Vectorworks assigns line weight and line style to objects.