To use Pentaho Metadata Editor, you must have database administrator skills (such as knowing how to import tables, create relationships between tables, assign aggregations, add categories, assign security, etc.) and extensive knowledge of your database(s). You must also know what type of data interests your business users so you can determine whether a column should be a measure or a dimension, for example. These skills allow you to map a business user model (logical model) to a complex relational database. Ultimately, the metadata models you provide to business users allows them to create Pentaho reports without requiring DBA assistance.
See Examining the Default Metadata Model for information about how metadata models are implemented in the Pentaho BA Server.