A very good question italki's explanations are ambiguous and are the reasons people can't understand the difference, especially between notebook and answers. The English language is not clear, I can not speak for other languages.
But it seems you just post a discussion into the discussion section for people to discus your topic.
You write notebooks that people can correct a bit like doing homework or an assignment from your teacher. Italki gives recommendations on the things to write about.
The Answer section is where you ask questions on anything such as what does this word mean I have never heard it before and people will mostly reply that is a slang word in country X or an Idiom.
You are right it is difficult for a language learner not to be able to pick out these subtle differences when they are still novice learners. It is not the novice learners fault.
For example on each page about these sections there is written text that contradicts what is written elsewhere on other explanation pages. It seems to be a case of the copywriters forgetting what was said on another explanation page and not making the various different pages agree.