The Langlands program is a set of conjectures, proved in special cases, about profound connections between different areas of mathematics. One of them being the theory of automorphic forms. I will give an introduction to automorphic forms and automorphic representations, aimed at being accessible to anyone and without requiring any background knowledge. In particular, we will see how holomorphic modular forms can be described as automorphic forms on adele groups, which provides a more conceptual viewpoint and also allows the application of strong theorems formulated in this context. As an example of such a theorem, I will explain Arthur's multiplicity formula, which describes the discrete automorphic spectrum. If time permits, I will present a result of mine regarding the linear independence of Siegel theta series in which I used the multiplicity formula.