Make sure you have a CRM Form Configuration and a TPC Form Layout already attached and configured. This would reveal the Attributes available to the Entity Selected in the Form Configuration.
Drag and drop the Pick List from The Portal Connector tools into the TPC Form Layout and click edit to display the properties prompt.
The Title will allow you to set the label for the control. By default it is set to the whichever attribute you choose but it can be freely modified.
The Attribute dropdown list allows you to select an attribute for the widget to submit data to. The pick list will be populated by the options associated with the attribute.
The Read Only option will not allow the user to interact with the widget when checked.
The Hidden option will hide the widget from the form when checked.
The Required option will not allow the user to submit the form until they've populated the widget with data.