A shared schedule is a schedule that can be used by more than one job. For example, you might have a predefined "weekdays" schedule for jobs that executed Monday through Friday. When you create a new job that needs to run on weekdays, you can link it to this shared schedule, rather than having to define a new schedule for the job.
Note that the shared schedule only defines the days on which jobs should run; each job has its own settings to determine the time(s) at which it should run.
Shared schedules are used on the Date Selection page of a Schedule.
Use the settings on the Security page to specify which users are allowed to use this schedule.