Achieving the precision necessary for a full understanding of heavy flavour physics requires a grasp of nonperturbative QCD (Quantum Chromodynamics) in heavy meson decays. Therefore, in this project, we delve into the nonperturbative QCD properties of certain heavy meson decays, pursuing research along two primary directions. In the first direction, we investigate nonperturbative QCD effects by using the method of nonlocal condensates in processes which are especially sensitive to underlying nonperturbative dynamics - in mixing of D0 neutral mesons and in rare D-meson decays. We aim to resolve a significant discrepancy between the measured D0-meson mixing parameters and their perturbative predictions which suggest a four orders of magnitude smaller result. Using the same method, we will pinpoint the nonperturbative QCD effects in rare D-meson decays which are influenced by underpinned nonperturbative dynamics, thereby offering predictions for present and future colliders. Secondly, our research focuses on understanding nonperturbative dynamics in selected heavy-to-light B- and D-meson decays, with the aim of overconstraining the Vub (and Vcd) CKM matrix element. This will be achieved by accurate determination of form factors using the light-cone sum rule method. Additionally, investigating B(s), D(s) -> eta, eta’ semileptonic decays enables us not only to determine precise branching ratios for these decays and extract CKM matrix elements, but also to extract the eta-eta’ mesons mixing angle. By combining the obtained form factors with available lattice QCD data, we can test lepton flavour universality in these decays and probe the Standard Model with great precision.Overall, this research contributes to our understanding of nonperturbative QCD properties in heavy meson decays, providing valuable insights into the Standard Model and beyond.