Meiosis is a two-step process that results in four haploid cells from one diploid cell. In meiosis I, homologous chromosomes separate and move to opposite poles. In meiosis II, sister chromatids separate to form four haploid cells each with half the number of chromosomes of the original cell. Meiosis involves pairing of homologous chromosomes and genetic recombination through crossing over, resulting in genetic variation in gametes. Meiosis is essential for sexual reproduction as it restores the diploid number when gametes fuse during fertilization.