Once you create your account structure, you'll then want to set up your terms with access dates. The basic function of a term is to give courses a start and end date. Terms can be manually added or imported by the SIS.
Canvas automatically comes with a "default" term which starts and ends from 'whenever' to 'whenever'. As your instance grows you will continue to add terms and define access dates. If you do not set an access date, users will be able to access courses based on default term dates inherited through the SIS.
Access dates are like terms, in that they determine when users can officially access the course. The instructor can override the term dates for a particular course, giving them the ultimate authority over their teaching and learning environment.
At the end of the term, courses will automatically 'conclude'. This means that the course is placed in an archived, read-only state. Instructors still have access to the course content You, as the Canvas Admin, can restrict student access to content only.