Once you add Form section to widget it has only Submit button. To add an element to the form, click the “Add content” button.
Select fields from list of available elements and add by clicking on them
To move fields point the mouse at the dotted icon, left-click, and drag the field up or down without releasing the button. To delete the field click on the delete icon.
Step by step option allows you to have only one form field shown on a widget at a time. The user will have to fill it out and press the Next button to move to the following field. This option is perfect if you have several required fields but don’t want to overload the widget design.
Read more about form fields customization here: How to customize form fields?