Hi Annisa, best to explain is to use an example. Imagine you have service with 60 minutes duration, slot step 60 minutes and you put working hours from 08-11 then you will be able to book appointments from next time slots:

08:00-09:00 09:00-10:00 10:00-11:00

If in same example you lower slot step to be 30 minutes then booking options will look like:

08:00-09:00 08:30-09:30 09:00-10:00 09:30-10:30 10:00-11:00

Best regards, Nikola