Single line spacing means that the spacing between lines is the width of a line. Setting method: first select the paragraph to set, select the format in the menu, then find the paragraph, and set it in the dialog box that appears. Or, after selecting a paragraph, right click on it, select a paragraph from the shortcut menu, and set it in the dialog box that appears.
The first floor has explained the concept of line spacing. To set line spacing, first select the content to be set, "Format" - "Paragraph" - "Line spacing" - "Fixed value" - adjust it to the desired height in the right box.