It is preferrable to schedule Apex Jobs as an Integration User or another User record that isn't attached to a System Administrator user. If an Integration User has not yet been created, schedule these jobs as System Administrator now and when an Integration User is established, reschedule them with that user account.
Click Setup, Search Scheduled Jobs, Select Scheduled Jobs
Click Schedule Apex
Label with a Job Name, typically use something very similar to the actual Apex Class that is going to run
In Apex Class, search and select the first job listed above to schedule
Determine frequency, in most cases Select Weekly, Click checkboxes for Monday - Friday
Start Date should be today or tomorrow
End Date should be as far out as possible
Preferred Start Time should be set as preferred; typically overnight so it's not running during the work day
Click Save
Repeat steps for all jobs listed under Apex Jobs to Schedule