Causal relationships are fundamental to the way we think about the world und understand it. However, the mathematically formulation of causality has only started relatively recently and is still under-way. This primer will start with a general introduction into the field of causality and the causal hierarchy, mentioning questions associated with all rungs of it. We will briefly introduce structural equation models (SEMs) and Pearl's do-calculus. Furthermore, we will discuss different approaches to identify causal relationships from observational data and introduce different methods for estimating causal effects.