Every page has an associated talk page, except pages in the Special: namespace. If nobody has ever posted on a talk page, then the link will be red. You can still discuss the page - you will just be the first person to edit the talk page.
Accessing a talk page
To access a talk page, look for a tab labelled Talk, Discussion or Discuss this page. These links will be found either at the top of the page or on the left hand side (near Edit this page).
The namespace of a talk page is Talk: with the page's title after the namepace. If the main page has a prefix then talk is added after this prefix.
If someone leaves a message on your talk page, the alert "You have new messages" is automatically displayed on all pages you view, even on other Wikias, until you view your user talk page.
Using talk pages
You should sign and date your contributions on all talk pages by typing four tildes: (~~~~), which will yield something like this: Example 19:07, February 18 2020 (UTC).
The "Post a comment" feature (the small "+" sign on a separate tab, at the top of a talk page) allows you to start a new section without needing to edit the whole page. The section header becomes the edit summary at the time you save the page, so there is no edit summary displayed when you use this feature.
If you are the first to post a comment, you don't have to do anything. However, after this, it is recommended you use colons (':') at the start of your comment. For example:
How's the soup? --John :It's great!! --Jane ::Not too bad... --George :::I made it myself! --John I think the soup-discussion should be moved to Talk:Soup... --Jane :I tend to disagree. --George
Doing so will produce this: