In Chapter 7 of Things Fall Apart, what do the stories told by mothers and fathers show about the villagers' belief system?

It is evident from the passage that you are refering to
that the tribal belief system is one that is not sophisticated scientifically, and still
uses parables, fables and myths to explain the world around them. However, it is also
clear that these stories have a valuable role in the socialisation of the young, or the
way that they learn the received culture of their tribe. Note what we are told about
Okonkwo's son and how he regards the stories that his father and mother tell
him:

So
Okonkwo encouraged the boys to sit with him in his obi, and he told them stories of the
land--masculine stories of violence and bloodshed. Nwoye knew that it was right to be
masculine and to be violent, but somehow he still preferred the stories that his mother
used to tell, and which she no doubt still told to her younger
children...

These stories are
fables about animals, and seek to explain the natural world in which they live. Thus we
can see that both sets of stories have their purpose in terms of socialising the young
of this tribe and also indicating the primitive belief system that the tribe
have.