Here You are just adding an event to the default Calendar . The event is added , once you call this function.
Simply Create an Object of EKEventStore
EKEventStore *eventStore = [[EKEventStore alloc] init];
and call your function :-
[self reminderWithEventStore:eventStore];
But you are not returning anything in your non-void function :) , but , the function definition is already documented in iOS API version 6 for EKReminder Apple, which is a class Method.
+ (EKReminder *)reminderWithEventStore:(EKEventStore *)eventStore
are you trying to override the above method.
You can simply add a reminder in the calendar using above class method.
First you should be clear of your motive , whether you want to add
1 Event
2 Reminder
3 Calendar.