To create an association relation between two elements, first select "Association" in the menu and after click on one element (class, actor or use case) of the relation, and after on the other element of the relation. The following DialogBox appears to fill information on the association relation.
The fields are the following:
In the Name Fields Area
In each class Fields Area (fields from and to)
A click on the "ok" button generates the corresponding element in the
Diagram Working window.