Click the large "A" to choose a font color and you have to go to "Go Advanced" to choose a font size. Click on "Sizes" to choose your size. These choices are in the toolbar. It's pretty much like you would do it in Word.
Just a suggestion ... please pick a font color that is dark and has a high contrast to the white background. Some font colors used here are so light that I rarely read the posts because it hurts my eyes to try to see the font.