A field is a key in a content file that can take a value, for example
- title
- text
etc.
https://getkirby.com/docs/content/adding-content
The value of such a field can then be queried in a template:
<?= $page->title()->html() ?>
<?= $page->text()->kt() ?>
Well, I don’t know what is in your theme files, whether you have just added differently named files or replaced existing files.
The important thing is to understand that a content file with a file name home.txt, for example, is rendered with a template home.php if that template exists. If not, the default template default.php is used. Check out the first few chapters of the documentation to get an overview at least.
So if you now have the starterkit with its content and added some other templates with different names that do not relate to anything in the content file, nothing is going to change.
As as regards the stylesheets etc, you would have to replace them as well as explained in the folder outline above.