How about copying the text and image from Unit 8, which I think is very clear and straightforward, viz.:
The discussion tab (sometimes called the Talk Page) is an essential part of the WikiEducator environment and can be found at the top of every page. Every content page in WikiEducator has a corresponding discussion page. This space can be used to leave notes or start discussions about the page you are viewing. Talk pages provide a space for editors to discuss changes and make suggestions about the associated page. The talk page is the same as any page on the wiki and accepts all the wiki syntax and editing that other pages do.
When you raise this issue in Unit 8, you can introduce it with a phrase something like this:
In the previous unit/tutorial, we introduced the discussion feature. You will recall that . . .
Just a suggestion.