Clicking this icon will open the Equation Editor.
Here, an equation can be created by inputting LaTeX coding into the window. Various equation options are shown on the top of the editor. As the code is written, a preview of the equation is shown at the bottom of the editor. Pressing Ok closes the editor and places the equation on the page.
To edit an equation that has already been inserted, select the equation and click on the equation icon to open the editing screen.