The work patterns determine the days and hours that are worked by each employee. Go to Admin > Settings > Work patterns for a list of currently available work patterns. By clicking the work pattern name you can edit the work pattern.
To add a new work pattern go to Admin > Settings > Work pattern (dropdown menu) > Add. Give it a name that describes the pattern (e.g. Monday to Thursday, Monrnings only etc). The 'Sets of' number allows you to configure work patterns that repeat over a specific number of weeks and the 'start date' is the date that this pattern should start from. Even if the pattern repeats weekly it is useful to set the start date from a Monday.
To change a work pattern for an employee go to People > Edit next to the Employee name and update the work pattern to the new one and click submit.
You can also move large numbers of employees to new work patterns by going to the work pattern the employee(s) are currently assigned to (in admin > Settings > Work patterns > name of work pattern) and towards the bottom of the page is a list of all employees currently assigned to that work pattern. Simply change the work pattern for the appropriate employees and click submit.