  In this thesis we explore the vacua structure of type IIA orientifold (CY)
compactifications with fluxes, from the 4d and the 10d point of view.
  We start by reviewing type IIA Calabi-Yau orientifold compactifications with
fluxes. We consider RR and NSNS fluxes, and then add (non)-geometric fluxes. We
recall how the potential can be written as a bilinear expression and review the
main swampland conjectures involving these scenarios.
  Once the basics have been setted, we perform a systematic search of vacua,
using directly the 4d action. We focus first on the case with RR and NSNS
fluxes and then repeat the same game by including geometric fluxes. We find
several families of SUSY and non-SUSY AdS$_4$ vacua. We check which of them are
(perturbatively) stable and which have separation of scales.
  We then analyse from the 10d perspective the SUSY vacua derived in the 4d
effective theory. We comment on how an uplift to $SU(3)$ structure manifolds
does not exist unless the O6 planes are smeared. We go beyond this
approximation and look for an uplift in $SU(3)\times SU(3)$ manifolds,
considering only the case with RR and NSNS fluxes. To do so, we expand the
equations of motion in terms of $g_s$. At zeroth order we recover the smearing
approximation. We solve the expansion at first order, where the localised
nature of the O6-planes is taken into account.
  We use the same machinery to study the non-perturbative stability of some of
the families of non-SUSY vacua with only RR and NSNS fluxes. According to a
refined version of the weak gravity conjecture, there should be membranes in
the spectrum with $Q > T$, triggering its decay. We see that D8 branes wrapping
the internal manifold with D6 branes ending on them can satisfy this
requirement.
  We finish by recapping all the results and making some comments about which
questions are still open.
