Consider the forum to be a public one that is not formal, but not entirely informal either. Avoid overly casual language, including slang. Avoid obscenities entirely. Your answers do not have to be lengthy. Generally, write and submit one paragraph at a time.
Most assignments require several submissions that are about a paragraph each.
You must respond to the comments of others. Respond to others by reacting to a viewpoint they express, asking a question such as to clarify their position, and by providing another viewpoint in contrast to the one presented. Show evidence that you have read other people's replies in your comments. Incorporate references to relevant readings and authors often, but be sure to put your comments in your own words. Except under unusual circumstances, avoid quoting.