Plasma simulation models that use particles and that have been developed for studying the microscopic behavior of a confined plasma in a magnetic field are described. The first model is developed to investigate the anomalous diffusion of particles and energy due to low-frequency electrostatic microinstabilities in cylindrical and toroidal systems. The model makes use of the combination of eigenfunction expansion in one direction and the multipole expansion on a two-dimensional spatial grid for solving Maxwell's equations and for pushing particles. The second model is developed to study the neutral-beam injection heating of a tokamak plasma, taking into account the spatial variation of plasma parameters and the finite ion-beam banana orbit. The self-consistent electric and magnetic fields are totally ignored in this model, and the Fokker-Planck collisions on the beam ions due to background ions and electrons are built in through the Monte Carlo method.