hi, i'm confused in drawing FDD, i search a lot in google but i didn't get the right answer

the FDD it start by the system then all functions in my system then activites for each function and tasks for each activity.

Functional Decompostion Daigram (FFD)

i need you help to draw it for me . my system is e-commerce website for multi vendors . so, i want FFD for e-commerce contains the basic function in the e-commerce website like order, product , delivery, report gerenration .... etc