If i have a 5 page xara site just with text content, i create a new mythemes folder and publish my existing site to the mythemes folder.
Then within the CMS i need to create 5 categories, one for each page and add the text that was in each xara page to the the text area on each category in the CMS.
Then also create a placeholder on each of the xara pages with the {page_content} tag.
Is all of this correct ?
Yes, you can do it this way, if you want each page to be editable in the cms. But with this approach you might only need one page template in Xara with a {page_content} placeholder instead of 5. It depends if you want the pages to use the same page template or not. Generally speaking the less page templates you use the better. Eg. you could run an entire 100+ page website on just one page template.
Also some pages you might not want to update or add content to in the cms, in this case if you want to you can leave all the text and content on your Xara page. Without a placeholder on the page the cms will just show the page as it was in Xara without dynamic content. It's flexible and there are a few different approaches you can take.
How then does all the new content get picked up when i would enter www.mywebsite.com into the browser, whats to stop the old html files that are still in the public_html folder from displaying ?
The index.php file in public_html needs to have just the code below so it can run and display the pages outputted by the cms. Replace path_to_cms with the location of the cms directory. Also make sure there are no other index.htm or index.html files in public_html and rename or backup your existing files so you can restore it if need be.
<?php require_once("path_to_cms/scripts/cms_front.php") ?>
Bear in mind any navigation links on your page templates in Xara will need to point to the new page urls generated by the cms. Again make a copy of your websites .xar file so you can easily revert back if needed.
I'm just a little unclear how it all ties together at the end and i appreciate your patience in answering my questions
No worries, ask as many questions as you like, I aprreciate it takes a while to understand the different approaches and workflow.