Any PBworks Admin can define properties for the workspaces on the network, through the "Workspace Properties" setting in the network's Admin panel.  To access the Admin panel, click "Admin" in the network bar to access the settings:

Then, click on "Workspace Properties" on the left hand side. 

To edit an existing property, click the pencil icon next to the property listed.  A property can be removed from the network by clicking the red "X" icon next to the pencil icon.  Please note, that if a property is deleted from the network, the property is also removed from all workspaces.

To create a new property, click the "New Property" button in the settings and select the kind of Property that needs to be created.  Please note, that once created property types cannot be easily changed (without completely removing the data already inserted into the property).  So, if you need a property that specifies a date, it's best to use the date type, rather than relying on your users to properly format the date in a text field.

Note: Only the "Dropdown Field - Multiple Value" type of workspace property can handle multiple values for the same property.  While you can have multiple properties in one format (like "Date"), you can only define a given property once per workspace. This limitation is part of the technical design, and makes the property value you set meaningful for the workspace.

When defining a Dropdown Field, list your choices as one choice per line.  Whether you select "Single Value" or "Multiple Value" the values you list here will be the only choices users setting this property will be able to choose from.

Finally, when setting a property, you can also set whether or not the property is filterable, and part of the filter set on the left side of the workspace listing.  If you want your users to be able to sort workspaces based on the value of this property, check the "Make filterable" checkbox and save the setting.