This review article provides a comprehensive introduction to various classes of chiral string compactifications to four dimensions using D-branes and fluxes. The main focus is on constructing four-dimensional orientifold vacua to closely approximate the supersymmetric Standard Model (SM). The authors outline methods to derive the four-dimensional effective action and discuss recent attempts to address the string vacuum problem through statistical approaches to D-brane models. The content is divided into several sections, covering basic concepts such as D-branes, orientifolds, and intersecting D-branes, as well as model building techniques, low-energy effective actions, and flux compactifications. The article also explores the statistical approach to D-brane models and concludes with a discussion of the challenges and progress in string theory phenomenology.This review article provides a comprehensive introduction to various classes of chiral string compactifications to four dimensions using D-branes and fluxes. The main focus is on constructing four-dimensional orientifold vacua to closely approximate the supersymmetric Standard Model (SM). The authors outline methods to derive the four-dimensional effective action and discuss recent attempts to address the string vacuum problem through statistical approaches to D-brane models. The content is divided into several sections, covering basic concepts such as D-branes, orientifolds, and intersecting D-branes, as well as model building techniques, low-energy effective actions, and flux compactifications. The article also explores the statistical approach to D-brane models and concludes with a discussion of the challenges and progress in string theory phenomenology.