Multicomponent silicate and borosilicate glasses find wide technological applications ranging from optical fibers, biomedicine to nuclear waste disposal. As a common component of earth's mantle and nuclear waste, iron is a frequent encounter in silicate and borosilicate melts and glasses. The redox ratio in glass matrix defined by the ratio of ferrous and ferric ions is dependent on factors such as temperature, pressure, and oxygen fugacity. Understanding their roles on the short- and medium-range structure of these glasses is important in establishing the structure-property relationships which are important for glass composition design but usually difficult to obtain from experimental characterization techniques alone. Classical molecular dynamics simulations were chosen in this dissertation to study iron containing glasses due to challenges in experimental techniques such as NMR spectroscopy originated from the paramagnetic nature of iron. Magnesium is also a common element in the oxide glass compositions and its effect on the structure of boroaluminosilicate glasses were also investigated. Magnesium ion (Mg2+) has relatively higher cation field strength than other modifier cations and its structural role in oxide glasses is still under debate. Therefore, investigating the effects of cation field strength of modifier cations in light of MgO in boroaluminosilicate glasses is also an important goal of this dissertation. Overall, through detailed and systematic molecular dynamics simulations with effective interatomic potentials, the structures of iron and magnesium containing complex boroaluminosilicate glasses were obtained and used to interpret properties and their changes with glass composition for nuclear waste disposal and other applications.