Autofill Help

I'm trying to figure out how Microsoft made their Homework Schedule template (link: https://templates.office.com/en-au/Homework-schedule-TM00000021) but I can't seem to get anywhere. The parts I'm trying to figure out in specific are where you can enter the number of rows you want for each day and it'll set that and then the part where you enter a date and it will auto-populate the dates for each day for the next 30 days. Anybody able to help me with this?