All of the UML diagram types share common context menu commands. To use the context menu for a diagram, simply right click in the Diagram view.
To view the common context menu commands, see Common Diagram Context Commands.
The class diagram context menu shares the common context menu commands as well as commands specific to it:

The New command for the class diagram offers a submenu with the following options:

Selecting Class from the submenu adds a class element to the diagram.
Selecting Interface from the submenu adds an interface element to the diagram.
Selecting Package from the submenu adds a package element to the diagram.
Selecting Object from the submenu adds an object element to the diagram.
Selecting Class by Pattern launches the Apply Pattern dialog displaying the available patterns.
Selecting Note from the submenu adds a note element to the diagram.
To refer to an element located outside of the current diagram, or to another diagram, you can use shortcuts. Invoking the Shortcut command displays a selection dialog, where you can choose the desired element (or diagram) from the appropriate location.
The Quality Assurance command for the class diagram offers a submenu with the following options:

Selecting Audit from the submenu processes audits for only the specific diagram. For more information, see Running Audits.
Selecting Metrics from the submenu processes metrics for only the specific diagram. For more information, see Running Metrics.
Once you've run metrics on a project or part of a project, you can save those metric results and view them whenever you like. Use this command to load a set of metrics results. For more information, see Saving/Loading Metrics Results.