One of the first principles of standard cosmology is that the universe is to a very good approximation homogeneous and isotropic on large scales. This justifies the use of Friedmann–Lemaître–Robertson–Walker

(FLRW) metric to describe the geometry of spacetime and different energy and matter contents of the universe as uniformly distributed perfect fluids. Using these ansatz the dynamics of background space-time can be obtained by Einstein theory of gravity. However,

clearly the universe is not perfectly isotropic and homogeneous. There are large scale structures (LSS) such as galaxies and clusters of galaxies. In fact, maybe one the most significant accomplishments of the early universe cosmologists is the development

of a semi-classical framework for early universe such as inflationary scenarios that can provide the mechanisms in which the initial conditions for LSS are generated from vacuum quantum fluctuations and through linear perturbations theory around FLRW metric.

In this talk, I will review the cosmological perturbation theory and how the quantum fluctuations undergoing these scenarios can seed the generation of the large scale structures and provide connections to present observables.