I am just wondering what the best way is to create a page within a website that allows a user with no HTML knowledge to update it themselves. For example what I'd like is a basic text file they could update that automatically changes the content of the page. I am still pretty new at making web sites so I apologize if this is too much of a newbie question.
You can use PHP to "include" a txt file. e.g. <? include "client-text.txt"; ?> But then the client still needs to know how to access and modify the txt file. Have you thought about using Wordpress? You could set the site up in Wordpress, and then add an author (your client), with restricted permissions so they can only edit their own pages/posts. See here for more on WP roles: http://codex.wordpress.org/Roles_and_Capabilities
Waht you are looking for is some sort of CMS soultion. I just ran into staceyapp.com whicih allows you to drop a txt file for contents. Pretty simpe set up and you can provide FTP access to users to the desired directories so they can change their txt file.
Joomla is your best choice if you have big plans for your site. Your client will have easy access to create section, categories and articles if you give them the proper access. They will not have to know one tag or code.
I would say use Contribute it allow you to create regions in which the user can update with access to files and not disrupt the rest of the design and coding
Yes, I think the best solution for you is CMS (Content Management System). It's easy to install because many web hosts now have autoscript installer. You can also google for finding out what CMS suits your needs best.