It is available to your students the evening prior to the first day of the term in which is your course runs, but only after you Publish it. (A button for publishing is at the top of the Home page in Canvas.) You can change this date by heading to Settings on the course menu, and then changing the "Starts" time. However, be sure the checkbox underneath labelled "Users can only participate in the course between these dates" remains enabled, or else the course will revert to the actual semester start/end dates. This and other information is available in the PDF attached.