The divider is used to introduce a horizontal rule to your form. It is useful for separating areas of your form to make it easier to read.
The HTML field is be used to output raw HTML on your form. HTML is entered using the standard Wordpress HTML editor.
The spacer is used to introduce a block of space to your form. It is useful for adding space to your form to make it easier to read.
The Text Editor field creates a WordPress content editor in the typical fashion used in Posts and Pages.