What is Wikispaces?
As mentioned above, Wikispaces is a free place for businesses, individuals, groups, and educators to create and edit pages. Think of Wikispaces like Wikipedia; one person creates the wikispace, and if another person finds that there needs to be an edit, as long as they have an account, they are able to log in and make the necessary changes.
What Are Discussions?
Discussions are comments or disagreements that a person might have in regards to the article. For Wikispaces, depending on what you have your page for - let's say an education class - the teacher might set up pages for different subjects or may have groups set up their own pages for an assignment or project. The same is true for say a work project between co-workers; the group leader might set up a page so that those members are able to view it.
When a main page has been set up, there is an area in which people can discuss the topic. For instance, for the class project, the main page might be the summary of the project and the goals that need to be met in order for the group to receive credit. In the discussion area, the students in the group might discuss ways on achieving these goals, by stating their point of view or discussing someone else's. This is particularly effective if say, the group members are not in the same city or the same state; this can also be true if a business worker needs to go out of town or if all of the employees work elsewhere.