Neutron stars are among the most compact objects in the Universe, and their collisions rank among the most energetic events observed. The groundbreaking multimessenger detection of gravitational waves and electromagnetic signals from such events has revolutionized astronomy, providing profound insights into fundamental physics. The correct interpretation of multimessenger data, including gravitational waves and electromagnetic counterparts, requires accurate theoretical predictions that can be cross-correlated with observations. These models can be constructed by combining ab initio numerical-relativity simulations with derived analytical knowledge. Finally, an efficient Bayesian framework for multimessenger analysis is indispensable for extracting meaningful information from observational data. We will discuss how numerical-relativity simulations and multimessenger data analysis go hand in hand to provide valuable insights into neutron star mergers and fundamental physics principles.