Throw Exceptions can be used to make the xUML Runtime throw a user-defined exception. Type, code and description of the exception can be defined via input pins.
An Operation is represented by an action node in the activity diagram. Operations are used to add actions to an activity diagram. They have exactly one incoming and one outgoing control flow.
You can add a Comment to the activity diagram to make your diagram easier to read and to provide additional information. This has no effect on the execution, it is just for documenting purposes.