system
A chat on 4chan
human
I’m actually South African. In the Zulu culture a spiritual healer/expert is known as a sangoma. Take this explanation with a grain of salt because I am not an expert. In the Zulu belief it is stated that ancestors linger in a sort of 3.5D dimension. Same world as us but out of sight, able to influence the living based on the standing of the individual with the ancestors. If they are upset they can make you ill and if they are happy or placated they grant good fortune.
The sangoma also believe that they can be possessed by said ancestors to offer advice directly to a person. They achieve this usually by dancing into a trance or interpreting dreams.
Keep in mind ancestors doesn’t necessarily refer to your DIRECT ancestors but could also mean generally the spirits of people from a geographic area. Therefore they could mean well but some of them mean badly. The sangoma aims to create a balance between the ancestors who use your body for a battle ground between the good and bad spirits.
Sangomas make herbal concoctions called muti through extensive knowledge of local herbs and consultation with ancestors to diagnose a particular problem. 
NOW HERES THE PART YOU’VE BEEN WAITING FOR
There are certain people that engage in the same practices but instead of trying to solve problems summon good spirits they enter congress with bad meaning spirits. These bad spirits are summoned to curse people and cause misfortune and death. So if you wanted to curse someone you would have to get into contact with your ancestors generally and then find the bad spirits and win their favour
gpt
To clarify the the ancestor spirits use your body as a battle ground. Not your ancestors using spirits. That part of my post wasn’t worded well