This is the 'header' of a 'New Discussion' preperation window...the only difference on a 'Reply Post' header is the subject is already filled in. For the instructions here, we're only concerned with the 'Toolbar', which is the same in both.
And we'll start with 'font' instruction...
Be careful not to 'click' anywhere on the message area before you're finished using all the font options you need, or the highlighting will clear, and you'll have to rehighlight it.
Click on 'Font Style' to show the drop menu and click on the one you want...
Click on 'Font Size' to show the drop menu of choices...
Click on the to show the drop menu of colors available...
Now you can click inside the message area to clear the highlight and see how your choices have changed the look of your text...
The 'Paragraph' may take a little practice, keep in mind, like the 'indent' buttons, works either on the line that your cursor marker is left on, or on the text that is highlighted...