This window is accessed from the top menu, World → Show Owned land. It displays a list of the parcel(s) you own (if any), and how much land you contribute to groups.
The list of parcels you owned is organized in colums, showing the name of the parcel, the region in which it is located, the type of region, and the parcel size in sqm.
The buttons below this list:
Then comes a list of your land contributions to the groups you belong to. For each group listed, the sqm tier42) is given, if any.
Finally, some informative text:
Allowed land holdings at current payment plan: Shows the total amount of allowed m2 you can hold (privately owned or contributed to group) from within your current tier level.
Current land holdings: Shows the total m2 you currently own, including contributions to groups.
Available for land purchases: Shows the remaining m2 available within your current tier to purchase or contribute to groups.