Types cannot be created with AgileJ StructureViews; in fact none of your Java source cannot be modified in any way using this tool. Therefore, a diagram is just a reflection of your Java source, any types must already exist and be accessible to an open Eclipse Java project for them to be added to a diagram.
The only editing which can be done to a diagram is the choice, positioning and filtering of types on the canvas.
Diagrams support multiple selection of top level types, and single selection of inner types and members. Inner types and members are made selectable so that their connecting lines can be easily traced. When selected, top level types may be repositioned by dragging, or removed from the diagram by pressing the delete key. Choose AgileJ->Select->Invert Selection to deselect all selected classes, and select all unselected classes.