A diagram is a representation of the components or elements of your model and, depending on the type of diagram, how those elements are linked or how they interact.
When you first create a project, Enterprise Architect provides simple examples of diagrams appropriate to your selected model patterns, with annotations. You can edit these diagrams, and create additional ones.
Click on your new package and, in the Project Browser window toolbar, click on the New Diagram icon .
The New Diagram dialog displays.
Click on a diagram category in the Select From panel, and a diagram type in the Diagram Types panel, then click on the OK button. Enterprise Architect adds a diagram object to the package, with the same name as the package. It also opens the Diagram View for your diagram, in the center of the screen.
Now add some elements.
Click on the link for additional information on adding diagrams to a project.