So what I want is this:

A code that creates a text field that the viewer can put text into, then a button underneath it to submit that text into another code and redirect to a new url.

Like this


(Button would be here)

In this particular instance, I want this button to take the user's ID (which they entered) and put it into another code, the post that code as a reply to a forum.

Can someone help me with this please?

To make the text field and submit button you can use INPUT elements: http://www.htmlhelp.com/reference/html40/forms/input.html

How to redirect to another URL depends on if your web host allows server-side scripting (e.g. PHP) and how important security is.