Upon succession, all titles held by the late ruler will be divided amongst their eligible children, with the player heir always being given the primary title, realm capital, and any direct de jure titles associated with it.
New titles may be created for younger realm heirs. Under confederate partition, your titles will be divided equally between your children. Losing duchies, kingdoms, and empires on death is a bummer. That means if a second title gets created equal to the main heirs title, the nation becomes divided. It is pretty succession law because once the ruler dies, new titles might be created. Most of the nations in 866 start, have the confederate partition.