Nowadays many different physical structures, such as crystal structure and hydrogen atom structure, can be modelled using group theory methods. This paper mainly focuses on four aspects: infinite groups in general, the irrecognizable infinite groups, cosets of infinite groups, Sylow's theorems and the Sylow tower group. In this research, different fundamental aspects of group theory in linear algebra and their applications in both finite and infinite groups are explored. The definition and examples of groups are first given, and the irrecognizable infinite group is then introduced. In addition, the concept of cosets of infinite groups is explained with the definition of subgroups, especially normal subgroups, as well as the Lagrange's theorem. Lastly, Sylow's first, second and third theorems, and the properties of Sylow tower group are also demonstrated. Therefore, readers are able to use the knowledge of groups to analyse symmetric mathematical phenomena since group theory can be described as a study of symmetry.