Another use of graphs to represent information is in entity-relationship diagrams, or E-R diagrams. The creation of an E-R diagram is typically the first step in the development of a relational database. E-R diagrams have different types of vertices, which are typically represented by different symbols. One type of vertix, which is typically shown as a rectangle, represents entities; a second type of vertix, typically shown as a diamond, represent relationships between the entities; a third type of vertix, typically shown as a ellipse, represents properties of either entities or of relationships between entities.
E-R diagrams will be covered in great detail in the database course. In the meantime, please read the wikipedia entry on E-R diagrams at http://en.wikipedia.org/wiki/Entity%E2%80%93relationship_model.