Note: Parcels do not show up unless you are zoomed in on the map.
To turn on parcel labels, click on Layers tab:
Now you can turn on the checkbox for Label – Parcel Number:
Since this is a toggle button, you can just uncheck it to turn it off again.
You can also choose to label parcels by Owner Name, Site Address, or All Three (Parcel Number + Owner Name + Site Address).