Classic SharePoint site templates are built to utilize as much of the out of the box features of SharePoint as possible with custom coding and configuration for enhanced functionality and experience.
You may use tools such as SharePoint Designer and Visual Studio Code to modify the templates.
Sites created from the templates must be deployed to a “Site”, formally called “Site Collection” with custom scripting enabled. A separate “Site” is recommended to host all of your custom site apps, instead of your main SharePoint/Intranet site.
A purchased site comes with email support, upgrades and enhancements.