The Discussion Forum organizes content and navigation around three core concepts: categories, topics, and posts.
Posts
At its heart, a Discussion Forum is made up of individual posts. Posts are single messages posted by an individual. Posts can be of any length and can include images, videos, or file attachments.
Topics
Posts are organized into topics. A topic is a collection of posts around a single idea, question, or issue. Someone asks a question, raises an issue, or sets up a discussion by creating a topic with their original post defining that topic, and then others respond with their own posts.
Categories
Categories are organizing containers for topics. A category can have one or more topics. All of the topics in a category are usually related to one another. A Discussion Forum can have one or more categories, like "Week 1" or "Questions about Homework 2" or "Reflection Assignment." There's a special type of category called a private category where only specific individuals assigned to that category can see messages, create topics, and post in that category.
Category Groups
You can also arrange categories into category groups, which exist purely for visual organization on the main Discussion Forum page. You can't post directly to a category group. Instead, you post to a topic which exists inside a category (which may be inside of a category group).