Once you have created a schedule you can assign this to your screens in two methods:

1. Individually for a singular screen - To do this, go into the screens tab and either click into screens name or click the edit 'pencil' icon. Then under 'schedule queue' press '+ add schedule to the screen':On the next screen, you can select which schedule you want to play from the dropdown list. When you are happy with your selection, click 'Assign Schedule' to apply this to your screen:

2. On mass for multiple screens - You can add a schedule to multiple screens at once by simply going into the screens tab, clicking into 'Actions' then selecting 'Update Schedules for Multiple Screens':

You will then see a list of all your screens, where you can search and filter the screens (by name, location or tag). Click into the screens you wish to update, then select a schedule you wish to apply to them and a start date for the schedule (leave blank to schedule this in for the current date/time):

Once you are happy with this, click 'Apply Schedule' and this will push the schedule to all of your selected screens. 

You can also either of the methods above to schedule in advance to create a 'Schedule Queue' by changing the start date to a date in the future.