You need to publish your course before your students can access it. You can do this by clicking the Publish button on your Canvas course Home Page.
When it shows like the screenshot below, it means your course is published.
Please note that this may not show your course right away. By default, courses are available between the Canvas Access Dates for the listed term. You can modify the dates to give students early access to Canvas (how-to link), or extend their access once the course is over (how-to link).