Instead of multiple discussion topics (aka threads) within a forum, this only has one. Each person posts by responding to someone else's post.
Example: Julia simply wants to find out what cooking equipment the students own. Julia posts the first question and students respond to her. She can see all responses in one screen.
Each person posts one discussion
Each person starts their own discussion topic, and then others can respond to it.
Example: Julie wants each student to start their own discussion topic and use it to post a recipe they've written. Then students will try a peer's recipe and leave feedback by replying to the recipe author's topic or thread. Each student has a topic that's "theirs".
Q and A forum
The instructor begins this forum by posting a question. The students reply back to her and answer the question, but they cannot see anyone else's response until AFTER they have posted themselves.
Example: Julia wants to make sure the students have understood the reading. She posts the question "How long does it take to boil a pot of water?". Student post their responses without seeing what anyone else has answered. After they post, they can see if they were in agreement with their classmates or not.
Standard forum for general use
The most generally useful forum type. Anyone can start new discussion topics, or respond to an existing one.
Example: Julia asks the students to reflect on learning how to boil water. Students can post their reflection by starting a new discussion topic, or responding to another's post. If they want post something along a different train of thought, they can create additional discussion topics.
Standard forum displayed in a blog-like format
Same as above, except on the first page of the forum you will see the full text of the first post in each forum.
Example: Going back to Julia's recipe posting forum, she could use this format so the students could see the full text of everyone's recipes at a glance without having to click into each discussion topic.