It is possible to include a legend in your diagrams and views. A legend displays the types of elements that appear or may appear in the active diagram or view. Legend is one of the graphic shapes in the Create pane. 

Steps:

1. In the Create pane, in Graphic shapes, click  Legend.
   
   
2. In the Legend Setup window, select the desired layout of the legend: Vertical layout in one column, or Horizontal layout with x rows. Example:
   
   
   
   
3. Optional: If the legend should only show the types of elements that are actually present in the diagram or view, select Only include the types that actually occur in the view. If not selected, all types of elements that may appear in the active diagram or view (because the type of the diagram or view allows their presence) will be shown in the legend.
   
   
4. Click OK to generate the legend.

To remove a legend from the diagram or view, click the legend and press Delete. To change an existing legend, remove it, and then create a new one.

Example of a legend in an ArchiMate^® Application usage view