If you have 20 fields on your form, but want your users to fill only 15 of them and other 5 to be only available for admin then, 

please, see below how to hide field from form widget:

- Go to the Form widget menu and open Fields tab.

- Disable fields to hide or make them Read only.

You can also change the column's name on the widget.

Read how to hide columns on the Table widget here