The knowledge of the structure of the real solids is required for achieving the desired architectures in the research of new materials and/or optimizing the relationships between structure and properties. Understanding complex oxides needs accurate characterization at different length scales and the combined application of all solid-state techniques. Deciphering the relationships between all this information provides codes that allow the identification of the different structural levels, their roles and the way they interact. These step-by-step routes are illustrated through two basic mechanisms of solid-state chemistry: to determine the building units of one complex oxide in order to predict the existence of other arrangements on the one hand and to correlate complex ordering phenomena, such as those involving charges, orbitals and spins of manganese atoms in perovskite-type manganites on the other hand.