A resource is an item or object that a teacher can use to support learning, such as a file or link. Moodle supports a range of resource types which teachers can add to their courses. In edit mode, a teacher can add resources via the 'Add an activity or resource' link. Resources appear as a single link with an icon in front of it that represents the type of resource.
Here is a brief descriptive list. Each Resource type also links to the Moodle community's documentation for more information.
Book - Multi-page resources with a book-like format. Somewhat complex to set up.
File - A picture, a pdf document, a spreadsheet, a sound file, a video file
Folder - For helping organize files and one folder may contain other folders
Label - Can be a few displayed words or an image used to separate resources and activities in a topic section, or can be a lengthy description or instructions
Page - The student sees a single, scrollable screen that a teacher creates with the robust HTML editor
URL - You can send the student to any place they can reach on their web browser, for example Wikipedia