How Do I Link A Unit To A Building?

Go to Properties on the left-hand navigation, select Units from the drop-down menu and click on the Unit in question from the list. 

Once in the Unit profile, it will by default go to the Detail tab. Start typing the building you would like to link this unit to in the Estate/Building search bar, select the relevant building and click Save: 

Your unit profile will now be nested within that building!