Two kinds of kola are distinguished, and only one of them is used. Gbanja splits into two lobes and is the kola of ordinary chewing and trade. Obi abata splits into more, usually four, and it is the one that goes to the orisha and to the ancestors. The four lobes are read as two male and two female, which is the first reason the nut works as an oracle: it has a built in set of faces to land on.
The act itself is short. The nut is held, prayed over and named to whoever is being addressed, the lobes are separated, and they are thrown down. What is read is the combination of lobes falling face up and face down. The answers available are narrow, essentially yes, no, and ask again in another form, and that narrowness is the point. Obi is not for the questions Ifa handles. It is for confirming that an offering has been accepted, that a plan may proceed, or that a spirit being addressed is in fact present.
That makes it the most used oracle in the tradition and the least documented. A babalawo has to be found and paid; obi can be thrown at a household shrine in a minute by whoever is standing there. It is also the point at which almost every longer rite begins, so a great many ceremonies open with the same small question before anything else is said.