You use the Form screen to edit the form with all of its form elements (input fields, drop-down lists, etc.).
Click the green plus sign (3) in the structure area to display a list of all of the form elements available to you. Click a form element to add it to your form. This new element is inserted underneath the form element currently selected in the (1). You can use the search function (2) to search for form elements in the form tree. Click Add page (7) at the bottom of the screen to add another page to your form. This is also added to the form tree.
The bell icon (4) on the top right shows you how many form elements in your form (if any) are incomplete or have errors. If conflicts are present, the bell is coloured red. Clicking the bell opens a dialog that lists all of these errors. You can click one of these errors to jump directly to the affected form element.
You edit the properties for pages and form elements on the right-hand side. If you click Duplicate (6) or Delete (5) below this editing area, then you will duplicate or delete the form element that you currently have open.