Elaine (and keybored (thank you)),
Now I understand!
This is from the User Guide which you can download (4.3 MB)
here.
Structuring paragraphs
This section describes the different ways you can define the appearance of paragraphs. When in page view, all paragraphs appear within the margins you set (outlined as the gray line around the area of the page). When in draft view Nisus Writer Express allows your text to run as far to the right of the document window as you wish. The four blue paragraph definition "droplets" appear on the ruler at the top of the window.
Select the paragraph(s) you want to modify before making any changes to the ruler.
To set the indent or outdent (hanging indent) position of the first line of a paragraph:
Drag the First Line In/Outdent Indicator across the ruler and release the mouse button at the position where you want the first character of your paragraph to appear.

The First Line In/Outdent Indicator in various positions relative to the Tail Line Wrap Indicator
To set the text wrap area:
Drag the Head Line Wrap Indicator and/or the Tail Line Wrap indicator across the ruler and release the mouse button where you want the lines of your paragraph to wrap.

The Head Line Wrap Indicator in various positions relative to the First Line In/Outdent Indicator
You can drag the Head Line Wrap Indicator independently of the First Line In/Outdent Indicator. If you drag the larger, upper, the Independent Drag droplet, when you release the mouse button, the smaller, lower Conjoined Drag droplet bounces into position. The First Line In/Outdent does not move.

The Independent Drag Head Line Wrap Indicator droplet
If you drag the smaller, lower Conjoined Drag droplet, when you release the mouse button, the larger, upper, the Independent Drag droplet bounces into position and the First Line In/Outdent moves the same distance as you moved the Conjoined Drag droplet.

Moving the Conjoined Drag Head Line Wrap Indicator droplet

The Tail Line Wrap Indicator
You can select any combination of the four indents and line wrap indicators by pressing SHIFT or COMMAND as you click each one.
I hope this helps.