The graphviz vocabulary provides an interface to your existing Graphviz installation, thus allowing you to create, edit, and render Graphviz graphs using Factor. For more information about Graphviz, see https://graphviz.org.

This vocabulary provides the basic tools to construct Factor representations of graphs. For more details, see:
Graphviz data structures

Other vocabularies let you change a graph's look & feel, write cleaner code to represent it, and (of course) generate its Graphviz output:
Graphviz attributes
Graphviz notation
Rendering Graphviz output

After reading the above, you can see several examples in action:
Graphviz gallery