How to rig a character with bone automatic linking

Hi everybody! I just downloaded a nice rigged character from here: So, I am amazed at the cool things you can achieve with Synfig Studio, especially the bone automatic linking, but maybe I am missing some step because I cannot do the same as the video tutorial or as the rigged character’s file. When I try to link the parts of the character to the skeleton, some vectors are unaffected by the bones influence area; I have tried to follow the instructions of the youtube tutorial but I had no success on rigging a character. So, I hope somebody can please make a detailed tutorial to rig a character using bone automatic linking. Maybe someone can explain how was rigged the character from this file:
freechar.sifz (75.7 KB)

I am a Synfig fan, and I want to learn how to use all its marvelous tools, so please, someone explain to me how to rig a character with bone automatic linking.
Thank you, everybody!