Cknap, this site uses standard HTML tags for all that stuff. You can also just use the tool bar up above where you write your comments for stuff like bold, underline, and italics. I highlighted this sentence and hit the Bold button in the tool bar.
If you want to change the color of a sentence, like this, then use the color button on the tool bar (the capital A over the gray bar). The little drop down arrow next to it lets you pick a color.