Click the arrow to the right of the New Diagram 
icon on the Diagram view toolbar.
Choose the diagram type from the submenu.
Diagrams exist within the context of a project. Create or open a project before creating any new diagrams.
By default, diagrams are stored in the Together Model directory as XML files with the file extension *.txvDiagram_Type. For example, the file *.txvuse corresponds to a use case diagram, while the file *.txvseq corresponds to a sequence diagram. Choose from any of the methods below to create a new diagram in a project.
To create a new diagram from the UML Explorer:
In the UML Explorer view, right click on a source code package or the project root.
From the context menu, select New UML Diagram. The New Diagram Wizard displays. See, Using the New Diagram Wizard below for more information.
Alternatively, right click on the default diagram of a source package, select New Diagram, and choose the diagram type from the submenu.
The UML Navigator is not open by default. To open the UML Navigator view, from the menubar, select Window > Show View > UML Navigator.
To create a new diagram from the UML Navigator:
In the UML Navigator view, right click on a package or the project root.
From the context menu, select New Diagram and choose the diagram type from the submenu.
To create a new diagram using the New Diagram icon:
Click the arrow to the right of the New Diagram
icon on the Diagram view toolbar.
Choose the diagram type from the submenu.
To create a new diagram using the New Diagram Wizard:
From the menubar, select File > New > UML Diagram. The New Diagram Wizard displays.
Specify the properties for the new diagram as follows:
Location: By default, the new diagram is created in the package selected before the wizard displays.
Type: Use the drop down list to select a diagram type. By default, the Class Diagram is selected.
Name: Use the text field to type a name for the new diagram.
Click Finish.
If the Diagram view is already open, then the view is updated with the new diagram. If the Diagram view is not open, then it opens and displays the new diagram.
From a package diagram physical view, you can create a logical view of a class diagram. Changes made to one diagram are reflected in the other. To create a class diagram from a package diagram, right click on the package diagram, and select Generate Class Diagram from the context menu. The new class diagram displays in the Diagram view.