Understanding the "post/redirect/get" pattern

I am having a very hard time understanding the exact process of "post/redirect/get".

I have combed through this site and the web for several hours and cannot find anything other than "here's the concept".

How to understand the post/redirect/get pattern?

As you may know from your research, POST-redirect-GET looks like this:

• The client gets a page with a form.
• The form POSTs to the server.
• The server performs the action, and then redirects to another page.
• The client follows the redirect.

For example, say we have this structure of the website:

• /posts (shows a list of posts and a link to "add post")
  • /<id> (view a particular post)
  • /create (if requested with the GET method, returns a form posting to itself; if it's a POST request, creates the post and redirects to the /<id> endpoint)

/posts itself isn't really relevant to this particular pattern, so I'll leave it out.

/posts/<id> might be implemented like this:

• Find the post with that ID in the database.
• Render a template with the content of that post.

/posts/create might be implemented like this:

• If the request is a GET request:
  • Show an empty form with the target set to itself and the method set to POST.
• If the request is a POST request:
  • Validate the fields.
  • If there are invalid fields, show the form again with errors indicated.
  • Otherwise, if all fields are valid:
    • Add the post to the database.
    • Redirect to /posts/<id> (where <id> is returned from the call to the database)