Unconventional superconductivity often competes or coexists with a variety of complex material states. In cuprate superconductors, there exist states including spin order, charge order, the pseudogap state, and the strange metal phase. A comprehensive understanding of their relationship is fundamental to establishing the mechanism of high-temperature superconductivity. Spin dynamics in cuprates has been extensively investigated using inelastic neutron scattering, but charge correlations remain far less understood. The latest development of resonant X-ray scattering (RXS) has been able to detect charge correlations with unprecedented sensitivity. A series of RXS studies have revealed that there universally exist the charge correlations in cuprate materials, which covers a wide range of the phase diagram. Resonant inelastic X-ray scattering (RIXS) experiments further show the dynamical behaviors of charge order. These findings highlight the important influence of charge correlations on the properties of cuprates. In this paper, we review the latest research progress in the charge order in cuprates by using RXS, with a particular emphasis on RIXS experiments. Our focus is placed on recent works on dynamical charge correlations at high temperatures as well as uniaxial strain tuning of charge order. We discuss topics including the underlying interactions, microscopic structure and symmetries, and the possible influence of charge order on both the superconducting and normal states.