Permissions on specific entities and actions are set for a user group. An individual user inherits the permissions of the groups to which the user belongs. Transition rules further refine permissions by setting the changes (from what value to what value) that members of a group can make to an entity.
A user may have permissions that its groups do not have if the user owns the entity. Generally, the owner is the user that created the entity.
Permissions can be set on specific fields. See Fields and Lists.
References to Objects on Other Diagrams
CustomizationField on Fields and Lists