You can add shifts to an opportunity that volunteers can sign up for based on their schedule.
Calendar - where shifts for opportunities are built and managed. The Calendar has its own grid. You can view an individual volunteers schedule by going to the Volunteers tab, selecting the volunteer, and clicking "Calendar." You can create or view shifts for an opportunity by going to the Opportunities tab, selecting the opportunity(s), and click "Calendar."
Schedule shift / schedule slot - a volunteer assignment that has a start and end time. Shifts may be one-time, repeating, or a combination of both.
Schedule Shift Tutorial
This tutorial will teach you how to create a new repeating shift. (10 min)