In Smart School you don't have to create subscription fees for every months because student fees are not something like subscription billing which can be vary month to month depends on services usage. Student fees are pre decided at time of student admission so in beginning of academic session you will configure and create all fees for all students with their due dates. Although you can change assigned fees at any time of student because fees are calculated in real time.

To understand how Smart school fees collection module is working please check this documentation