The author, Rik, explains the process of explaining a graph model in an existing Neo4j database. He shares a query that generates a table showing the labels and types of relationships between nodes in the database. To visualize the model graphically, he tweaks this query to create a META-graph by merging nodes for each label and relationship, using MERGE statements. The resulting diagram is readable and easy to understand, making it useful for visualizing existing graph models and databases.