This sample is in our list. Could you elaborate on your use case? Do you have the vertices of polygon/polygons, and would like to calculate the area of the polygon?
A geometry sample is coming. In the meantime if you still have questions, you should use ArcGISPolygonBuilder to create the polygon. In order to visualize them, you can use Unity's line renderer . Think it as that Unity provides the way to render it and we provide the way to do calculation (like the area calculation you mentioned) and spatial analysis (such as intersect, union, etc.).
