What is a Template?
A WordPress template is a file created by your theme that determines the layout for a page or post. Templates contain HTML and CSS code that identify how content is displayed.
More About Templates
Most themes include standard templates. However, the exact templates will differ between themes. You will commonly find templates for the main page, the header and footer, sidebar, posts, and comments.
You can access template files by navigating to Appearance > Theme File Editor from your WordPress dashboard. You can edit the templates from the text box on this screen.
You can also use an FTP client to access your templates. You will find them in your theme folder inside the /wp-content/themes folder.
With WordPress block themes, you can also edit and add new templates from the Site Editor.