The customizable toolbar of the diagram tool can contain these buttons:
Target to cluster or class
Drop a class or a cluster on this icon to build the corresponding diagram.
Target to enclosing cluster
Recenters the diagram on the parent cluster.
Create a new class
Pick from this button and drop on the diagram to add a new class.
Create new inheritance links
Selecting this button allows you to create inheritance links by picking from one class and dropping on the other.
Create new client-supplier links
Selecting this button allows you to create client-supplier links by picking from one class and dropping on the other.
Create new aggregate client-supplier links
Selecting this button allows you to create aggregate client-supplier links by picking from one class and dropping on the other.
Delete
Drop items in this hole to remove them from the system.