This chapter is dedicated to preliminary and basic concepts of molecular dynamics with details on interactions of molecules with ideal or material surfaces and with particles carried by a fluid. The fundamentals of the Boltzmann equation and of the Maxwellian distribution function and the basic ideas about the Larsen-Borgnakke phenomenological method are also revised. This chapter, however, is not intended to be a textbook, but rather to be a compendium of the major topics dealt with in the subsequent chapters, thus sparing to the un-experienced young reader a tedious search of topics which would involve consulting several textbooks with different backgrounds. In thus far, it is appropriate to state that there is nothing original in this chapter, apart from the presentation which is intended to be essential and suited for the beginner. For this purpose one section has been dedicated to a review of several techniques available for sampling probability distributions. The chapter closes with a topic concerning future applications of aerosol particles in an environment simulating the upper Earth environment conditions. For this purpose is also presented the treatment of the equation of motion for droplets in a cloud and the impinging of droplets upon a hydrometeor of spherical shape in atmospheric conditions.