What is a presentation?
A presentation is a piece of content that can be shared out with anyone (as long as you don't have additional security settings enabled) and is commonly displayed on your Content page in Brainshark. Presentations can be created from the My Content tab of Brainshark if you have authoring permissions within your site.
What is a course?
A course is the same type of content, but to view it, the viewer must be logged into Brainshark. Courses are created and housed in the Learning section of Brainshark.
If a course is set to have "Open Enrollment", the course can be searched for in the Course Catalog and can allow students to enroll themselves in the course. If a course is set to "Limited Enrollment", an admin or the course's author (or a Learning Manager in some cases) must enroll the student or they will not be able to take the course.
Once a student is enrolled in the course, the course will display on their My Enrollments page.
When creating a course from an existing presentation, you are essentially creating a duplicate piece of content that is meant to work exclusively within Learning. The content will behave exactly how it does as a presentation to an end-user but would be recognized as a copy of the original presentation. In these scenarios, any changes made to the course created in Learning would not be reflected in the presentation it was created from (and vice versa).