After you installed GN4, you may want to configure / customize it, being the system out-of-the-box based on sample configurations and not necessarily appropriate for your particular needs.

Customizing may include, for example, adding more article elements, or additional attributes and objects to the schema; changing entry dialog and directory styles. Configuring may include creating or importing system users, folders, copyflows, categories, keywords, changing of measurement system, creating publishing and extract destinations etc.

The customizing is described in Customizing GN4 System for Your Publications. The configuring is described in Configuring GN4.