Dod,
When you add those special font [size=24]sizes[/size] and [size=36]
colors[/size] in the reply box where you type, it will only show the enclosed brackets and the numbers.
When you have finished your post [size=18]
highlight[/size] the word or phrase you want to change, choose the font size or colors and the brackets will show up around your highlighted words. Now, hit the [size=48]
preview[/size] button below. Scroll back up, and you will see how your post will look, once you actually post. When you are done [size=20]
previewing[/size], hit [size=22]
post[/size] and all will be what you hope it to be.

Tim