Ubiquitous in a wide range of nature processes and technologies, a subtle modification (e.g. structurally, chemically, or electronically) near an interface can have a decisive effect on properties of the collective as well as each individual. A compelling case manifesting such subtlety is oxide heterostructures and heterointerfaces exhibiting fascinating emergent behaviors due to numerous combinative contributions of atomic structures and chemistries, which can be effectively harnessed for the design of advanced materials for information and energy applications and accelerating materials integration into advanced devices. Surface/interface X-ray scattering from modern synchrotron sources integrated with phase retrieval direct methods provides a very powerful toolkit to decipher the interfacial subtlety. This is essential to our ability to provide a quantitative and realistic description of the interfacial boundaries by which to engineer properties of oxide interfaces using atomic structure-driven design principles in a reliable and controlled manner. In this seminar, I will firstly give a brief introduction of how to obtain atomic mapping of oxide heterostructure and heterointerfaces with sub-Ångstrom resolution by phase retrieving coherent Bragg rods, wherein complete atomically structural information hidden, in particular on the COBRA method in combination with the difference map algorithm achieving unprecedented speed of convergence and precision. In the following, I will demonstrate a few recent studies in the exploration of oxide heterostructures and heterointerfaces for information and energy applications by applying the direct method, such as revealing structural motifs responsible for 2DEG and superconductivity adjacent with heterointerfaces, catching structural perturbations in response to varied polar energy landscapes, differentiating at the atomic-layer level the complicated cation distribution relevant with creating new polar order and enhancing oxygen reduction activities, and depth-resolved mapping oxygen-octahedral connectivity patterns essential with incipient functionalities of heterostructures. In the end, I will give a short commentary on future opportunities in X-ray studies of oxide interfaces and heterostructures enabled by the exciting advancements towards ultimate storage rings, in particular with enhanced high-energy and coherence capabilities.