Ferroelectrics, a major class of high-coupling materials characterized by the switchable polarization, have become important in modern devices ranging from medical ultrasound, non-volatile memory to vibration-powered electronics. The device functionalities heavily rely on the interactions between the electric polarization and applied stimuli (e.g., electric fields). Understanding the dynamics of ferroelectric domains and domain walls in response to external perturbations is important for the development of ferroelectric-based functional devices. In this talk, I will firstly introduce a classical force field we developed based on the bond valence theory which enabled large-scale molecular dynamics simulations of typical ferroelectric materials at the million-atom scale. I will then explain a theory-experiment collaboration wherein we demonstrated deterministic and repeatedly obtainable multistate polarizations in ferroelectric thin films, highlighting the potential of ferroelectrics for adaptive neuromorphic electronics. Finally, I will explain how the resonance of domain walls can be exploited to obtain tunable dielectrics with ultralow loss and high tunability.