EF and map store procedure

i just read this article http://www.c-sharpcorner.com/UploadFile/ff2f08/call-store-procedure-from-entity-framework/

they show how they add store procedure to EF

i though when we select store procedure by entity data model wizard then i do not have to do anything to call the store procedure from code but this article showing later we need to doAdd Function Import . my question is when we select store procedure by entity data model wizard then why we need to go for theadd function import ?

please tell me can't we call store procedure just after selecting it without function import.

please guide me. why and when function import is required ?