Contoso is Microsoft's retail demo: a chain of stores selling products through several channels, with promotions. The sample .pbix is a public download.
What the drawing shows
Sales is the one fact table, on the middle disc, and the biggest dot: almost all of the model's stored data is in it.
Seven tables sit one join out: Channel, Stores, Promotion, Product, Geography, Calendar and the first product level.
The product dimension is snowflaked: Product joins ProductSubcategory, which joins ProductCategory, two rings out. The portrait makes a snowflake visible as rings, which a flat table list never does.
Four of the thirteen tables are the automatic date tables Power BI creates behind every date column. They carry long generated names and sit where their date column's table sits. Most models have them; most people have never seen them drawn.
The model has no measures: the sample's visuals use implicit aggregations. In your own model the measures appear as freckles on their tables.
Where to get the sample
Microsoft's download page for theContoso Sales Sample for Power BI Desktop. Export the two files with the steps on this site, or click the Contoso disc on the landing page to open it directly.