To use any images or documents, such as your course syllabus, you must first upload the files from the Files & Uploads page. Then you link to the uploaded files from a component within your course. Remember that without a link to a file, the students can't see it.
Here's how to upload a file for your course:
Here's a warning: if you upload a file that has the same name as an existing course file, the original file will be overwritten without warning.