Stochastic processes are families of random variables whose trajectories may differ with each realization, unlike deterministic processes, yet allow for analysis and simulation of dynamical systems, conserving some non-probabilistic quantities. This talk will be a rough introduction to some key concepts of stochastic processes, e.g. random walks, Markovianity and metastable sets. The latter typically correspond to almost independent substructures of the state space, such as functional subunits of a cellular network or stable conformations of molecules.