The interaction of intense laser fields with matter is accompanied by a multitude of phenomena, ranging from the generation of coherent radiation across various spectral ranges (from terahertz to soft X-rays) to the creation of beams of accelerated charged particles and micromodification of the volume and surface of various samples. To describe this diversity of phenomena, several theoretical approaches have been developed to date. These approaches utilize different approximations to address this complex nonlinear problem, allowing for the explanation of specific aspects of such interactions. The developed theoretical frameworks consider the interaction at both microscopic and macroscopic levels; at the microscopic level, they investigate the characteristics of single atoms interacting with laser fields, while at the macroscopic level, they analyze nonlinear susceptibilities that describe the nonlinear polarization of the medium during the propagation of laser radiation through it. This work presents an overview of methods describing some of the most commonly employed theoretical approaches to model the response of a medium at a microscopic (quantum-mechanical) level, as well as various methods for controlling the properties of generated coherent radiation. A model for the gas medium is described that accounts for both the response characteristics of individual atoms and allows for consideration of phase and quasi-phase matching effects during radiation generation. The influence of medium parameters on the efficiency of generation and polarization properties of generated radiation is analyzed under both phase and quasi-phase matching conditions. A detailed description of an analytical method for calculating the nonlinear susceptibility of a gas medium is provided. The obtained values of nonlinear susceptibility for arbitrary orders may be useful in numerical calculations concerning the propagation of laser radiation in matter. Various channels for radiation generation are analyzed as parameters of the laser field are varied.