An Enterprise Architect model is a top level (root) Package in a repository. It is possible to have more than one root Package in a repository and hence more than one model. Each model is the root node of a hierarchy of Packages, elements, features and diagrams that are nested under the Package. The Browser window is used to manage the model and the hierarchy of elements, features and diagrams, showing how the models are structured and helping you to reorganize a model by dragging and dropping objects to new locations in the hierarchy.
Enterprise Architect has a handy Model Wizard that helps you to create models and a hierarchy of Packages under each root, from a wide selection of model Patterns. The Wizard is displayed automatically when a new model is added to a repository, but can be invoked manually (Start Page 'Create from Pattern' tab). Using the Wizard simplifies the process of setting up repositories and models for the novice modeler. More experienced modelers are free to add a single Model Package and build up the structure as they see fit, or to create a model from a base (template) repository.
As your model develops, you can use the Model Wizard to inject fine-grained content into your overall model structure. A Package configured to manage Requirements, or one for Decision modeling, or Simulation of States or one of hundreds of other pre-built patterns that help you develop and refine your model for your domain and your project.
As the repository is developed and during the lifetime of a project or program of work, new models might have to be added and existing ones refactored.