When you're writing a post, you can make the html tags in it visible by pressing the 'html' button (the rightmost one above the reply box). This is particularly helpful if you want to put a "reply" quote at the start of your post. When you press the "reply" button immediately below a post you want to respond to, the board brings up a box with the post's text in a blockquote (at the bottom of the box). If you bring up the html, you can place your own text after the quote by placing it after the /blockquote instruction.
I sometimes write my posts in Word and then transfer them across. This can result in unwanted formatting effects, so when I do this, I switch to html format and cut out the chaff I don't want.