A Course is a set of lectures that can consist of any type of content (e.g. video, documents, presentations, etc).
A Curriculum is a group of courses, usually on a related topic. You can create a Curriculum if you want your employees to have a more comprehensive skillset on a topic or if you have a Course that is offered in different languages.
When you enroll in a Curriculum you will automatically get enrolled in all the Courses that are relevant to you, based on the language setup of the Curriculum.
When you attend a Course that is part of a Curriculum, it will automatically update your progress bar on the Curriculum's page. Therefore, every time you go to the Curriculum's page you will see your progress regarding all of the Courses you are enrolled in and the total progress on the Curriculum.