This 'how to' can be recreated in either NIntex Forms 2016, Nintex Forms 2013 or Nintex Forms 2010.
So you may have found yourself in this scenario - you've created your SharePoint list, and added a Nintex Form to the list. As you're designing the form, you realize you've forgotten to add in a column. Now you could exit Nintex Forms, go back to your SharePoint list and create a column through the SharePoint interface, or you could create a list column from directly within the Nintex Forms designer! I think I know which sounds better
To do this, you'll need to click on the Create Column button in the Nintex Forms Designer Ribbon.
The Create Column dialog will appear, enter the name of the column, and the type. Click OK.
The new SharePoint column will appear in the Form Controls Toolbox, in the List Columns category. Now you can add it to the Nintex Forms designer as you would any other control and continue designing the form. You will need to add a Label control next to the new List Column control when it's added to the form. During Runtime, information entered into this new control will appear in the SharePoint list.
What is the best practice? use Nintex form Controls or SharePoint Column? I noticed when you create SharePoint Column you are able to see that in the SharePoint list view, but when you use Nintex form control you are not able to see the column in the SharePoint list view. What is the advantage using one on another?
I got the answer from Simon.
Nintex forms does not create columns in SharePoint like Microsoft's InfoPath did/does as its a different product.
Columns should be created in SharePoint for any data that you want from the form to be entered into SharePoint.
Other controls can be added to the form to display information from other resources to give the user a richer experience but this information is not submitted to the SharePoint list unless a column is created for it and linked.
When using a default SharePoint form you can only use the controls relating to existing columns where Nintex Forms allows you to display more information that could assist the user in completing the form.
How can I add a managed metadata?
I created the metadata field following this instruction. but I can not the field listed under form control, I can see the the field was created when I check the List Settings.
Nintex support say that Nintex for Sharepoint online can not add Managed Metadata fields. only Nintex on primes can handle that, and its on Nintex Road map to add this functionality.