Marking Important Sections

To mark a section with a red box around it…

like this…
  1. Edit the page.
  2. Select HTML mode (top right of the edit box)
  3. Wrap the paragraph with divs as follows: <div class="urgent"> paragraph </div>
  4. Select Visual mode again.
  5. It won’t appear any different in the editor, but on the actual website it will work correctly.

That will put a red box around it. The style for that is defined in Appearance / Editor / Stylesheet, at the end of the file. Only change it if you’re reasonably comfortable with CSS.