The Standard Model (SM) of particle physics provides a robust framework for understanding the electromagnetic, weak, and strong interactions of fundamental particles. Despite its many experimental successes, it leaves several important phenomena unexplained, such as flavor mixing and the pronounced hierarchies in fermion masses; collectively referred to as the flavor puzzle. This article explores how fermions within the SM acquire hierarchical masses through the Higgs mechanism and Yukawa couplings, which in turn give rise to the Cabibbo-Kobayashi-Maskawa (CKM) matrix that plays a central role in flavor mixing. As one possible approach to understanding this hierarchical structure, the Froggatt-Nielsen (FN) mechanism is presented, introducing a horizontal ?$U(1)_x$? flavor symmetry together with a new scalar field, the flavon. The spontaneous breaking of this symmetry through higher-dimensional operators leads to new FN couplings that yield a natural explanation for the observed fermion mass hierarchy. Finally, the article examines the phenomenological implications of generic FN models at low energies, such as meson mixing, and discusses possible UV completions of the theory through introduction of vector-like fermions. The analysis indicates that consistency with experimental constraints requires a high energy FN scale, thereby providing insights into possible extensions beyond the SM.

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