Resources are course materials that students read but don't interact with, such as presentations, graphics, and PDFs. Resources are added from the "Add an activity or resource".
A Book is a series of web pages, organized into chapters. A Book can consist of one or more chapters. This is a good option for presenting a series of web pages, that you want the student to read in order.
Moodle can serve a single File to your student. If Moodle's built-in media player can play the File, you can configure it to automatically embed. Or, you can configure the File so that it downloads to the student's computer.
A Folder is a collection of files that you have added to the course. For example, you can have a Folder for each topic in a course, where you give the student all of the files needed to complete the exercises for that topic.
A Label is a text, graphic, or a media file that you put on the home page of a course. Almost anything that you can put onto a web page, you can put onto the home page of your course. You usually use a Label to describe or label the content around it.
A Moodle Page is a web page that you create using Moodle's web page editor.
A URL is a link to another place on the Web. Usually, you link to a page or file that exists outside of Moodle. But, you can link to a place inside your own Moodle site.