Around the edge of the window you can display one or several of the rulers, row and column borders. These are helpful for designing pages, setting margins and formatting tables.
Depending on the type of document you are editing, you may want different measurement markers on display around the edge of the document.
You may have as many or as few of these displayed as you wish. The default setting in letter documents is that the top ruler is displayed; in sheet documents that the row and column borders are displayed.
The top ruler button displays the horizontal ruler.
The side ruler button displays the vertical ruler.
The column border button displays the column (horizontal) border.
The row border button displays the row (vertical) border.
See Choosing the ruler measurement and Default ruler for details of how to set the unit of measurement used.