Dimensions represent the tables in the data source, and constitute the quantitative data in the model. The Dimensions tab is accessed via the Data Selections Panel; each dimension can be expanded to expose the hierarchies contained within them. The hierarchies represent the columns within the tables in the data source.
To add qualitative data to your discovery, you can add an entire hierarchy by clicking it. In this example, the Manufacturer hierarchy is being added to the discovery:
He were see that the Manufacturer chip was added to the item selection bar, and the Manufacturer hierarchy is displayed in the visual:
Dimensions are also displayed from the Filter tab, where you can configure filters for your smart discovery.