One of the most basic form of divination in the Yoruba system is that of obi divination. It (usually) consists of four pieces of coconut and, after the question is posed to Spirit, the way the coconut pieces land determines the answer. I say that this form of divination usually consists of four pieces of coconut because, in Yorubaland, it consisted of four kola nuts, and can also consist of four cowrie shells and or four pieces of coconut with four cowrie shells attached to them. I have even used coins when I didn’t have coconuts, though I have only done this with egun (ancestors), not orisas.
Obi divination is one of the forms of divination open to use by non-initiates, meaning one does not have to be initiated to one of the orisas to throw obi. Many practitioners throw obi to their ancestors and their warriors to get simple answers to questions, and initiates throw obi to their orisas for the same reasons, like asking whether someone can join their ile.
I have always found obi divination to be pretty easy (and it is!) but it can answer more complex questions, where the layouts can be read as odu and the patterns can mark ebos (sacrifices) to various orisas. I won’t pretend to understand all of this but I am reading two books that are excellent resources: Obi: Oracle of Cuban Santeria by Ocha’ni Lele and Awo Obi: Obi Divination in Theory and Practice by Baba Osundiya.
One of the things both books emphasize is that divination is not a fortune-telling tool; when we come to the Spirit asking questions regarding our lives, the divination practice opens up these spiritual energies and gives them access to our lives. We thus exchange energy with them and become accountable to their wisdom and guidance, even, and possibly especially when, we receive information we do not want to hear.
I have used obi with Elegba, using the coconut/cowrie shell obi that increases the five possible answers to nine and everything was so spot on. I was so nervous when first divining with Elegba but I believe when we approach Spirit with reverence, humility, and truth, we have no need to worry.