PowerCMS stores the content of your site in a database table.
After installing PowerCMS, you would enter the admin, and then for each page you need to edit, you could copy the content from it, and paste it into the editor in PowerCMS. You then replace the content in your page with the code that PowerCMS gives you.
This is pretty documented in the tutorials, and the video showing the features of PowerCMS.
Is that what you were asking?