Each structure element on the canvas is called a node. Node is a general term that can represent a module, placeholder or object.
A module is an organization element that can represent different chapters, units or sections of your course. You must create a module in Course Builder before you can begin adding objects and placeholders.
A placeholder is essentially a container for an object. It is not visible to students until you add an object to it. There are five placeholder types: link, file, discussion, dropbox, and quiz.
Placeholders help you define the structure of your course before you're prepared to compile actual course content. This enables you to plan your lectures, discussion topics, assignments, tests and other course activities before you begin creating them.
You can populate placeholders when you’re ready by creating new content or linking to existing content. For example, if the completion of a particular course unit depends on acquiring files from another resource, drag placeholders onto the canvas to represent those files until you receive them.
Objects are simply learning materials, activities or assessments in your course. Object types include: links, HTML files, discussions, dropboxes, quizzes, grade items, and learning objectives.
When you create an object in Course Builder, you are in effect creating it within its respective tool and adding it to your course content. For example, when you drag a quiz object onto the canvas from Create Objects, Course Builder prompts you to enter its basic details and creates the quiz in Manage Quizzes. At a later time, you can go to Manage Quizzes to edit advanced quiz properties and add questions.