Dark matter halos are the major composition of the cosmic structures in our Universe and, therefore, play a central role in studying galaxies and cosmology. In cosmological N-body simulations, dark matter halos can be investigated from three perspectives: their structures, assembly histories, and spatial clustering. This talk will focus on our recent work on this topic. In the first part, I will introduce a new method to estimate the concentration parameter of simulated dark matter halos and demonstrate its superiority in efficiency and robustness over other methods. The second part of my talk will be devoted to a new method to characterize the assembly of dark matter halos by quantifying the spatial extension of their progenitor halos across cosmic time, named the protohalo size history. I will show that the protohalo size history strongly correlates to the central-to-total stellar mass ratio, which, in turn, can be deemed an observational proxy of the protohalo size history. In addition, the protohalo size history exhibits a strong halo assembly bias signature, which, combined with the observational proxy, could be detected in galaxy surveys.
