Short Answer: PHP.
Longer Answer: Use a PHP page (which means you have to be running PHP on your webserver) to take the content of the page and add it to a database. When you create the HTML file, you collect all the database entries to create the page.
OR
Have each entry into the text box be saved as a new HTML file and when you build the page, just recursively include them all and you've got it all.
Longest answer: I'm not going to take that much time yet.
The problem I have with this is that you want to do something that could open you up to a LOT of security issues. If you don't even know where to start to DO this, I don't think it's a smart idea to plunge ahead, unless it's a private website that can't be accessed from the internet.
To answer you, finally: Form + PHP + MySQL = "Blog" - type page
-rock
