Page Template
Purpose: 
Page templates are primarily associated with static pages in WordPress. 

Usage:  
You can create custom page templates to define the structure and design of specific pages on your website. This allows you to have different layouts for different pages.

How to Use: 
When editing a page in the WordPress admin, you can select a specific page template from the Page Attributes section. This template will be applied to that page. 

Single Template
Purpose: 
Single templates are used for individual posts, pages, or custom post types. 

Usage:  
hey define how a single piece of content (post, page, or custom post type) is displayed. Single templates are used to control the layout of a single post when it is viewed individually.

How to Use: 
When WordPress displays a single piece of content (e.g., when you click on a post title), it uses the single template associated with that content type.

Key Differences
Context: 
Page templates are used for individual pages, whereas single templates are used for individual pieces of content (posts, pages, or custom post types). 

Application:  
Page templates are more about defining the layout for specific pages, while single templates are about controlling the display of a single piece of content. 

Selection: 
Page templates are selected when editing a specific page in the admin interface, while single templates are automatically applied when viewing a single post or page.