All conversations about a page should be put on its Talk page, and never in the article itself.
The "Talk" icon creates a new page named "Talk" as a subdirectory of the page from which "Talk" was called. For example, clicking on the "Talk" icon for this page would create a new page named "Help/Talk Pages/Talk."
The "Talk" feature allows users to move discussions about a page off the main page. It provides a forum for discussion of page content that is conceptually separate from the page itself, giving users an area in which to work out conflicts, ask questions, or generally talk with other users who have similar interest in the page subject. Some possible reasons for creating a "Talk" page:
The veracity of some content on a page is disputed. A "Talk" page could be created to discuss the page's content.
A user has a question about something on a page, but does not want to ask the question on the page itself.
A user wants to communicate with other wiki users about the subject of a page, for example: "Is the content on this page true?"
A user is desperately lonely, and wants to "Talk"
All of these and more are valid reasons to create a talk page! It's a part of what builds the wiki community, and what helps keep the information on this site relevant, correct, and up-to-date.