Computer simulations have become a valuable tool for expanding our knowledge in many areas. The steadily increasing performance of supercomputers or even desktop computers allows us to simulate bigger systems more accurately. However, proper predictions can only be obtained if correct models and theoretical approaches are employed. Therefore, this course aims to provide essential foundations for performing computer simulations and ways to avoid typical errors from misunderstanding employed approximations. The lectures will span various molecular modelling methods addressing problems from supramolecular chemistry to structural biology. The course will comprise theoretical lectures complemented by practical sessions exercising typical simulation techniques in each discipline.