In the present studies on quantum computer systems principles of a quantum logic gates and basic elements of quantum computers are described. The fundamental elements of quantum computer and mathematical backgrounds of suitable quantum computation processes are presented. Specially Toffoli quantum gate and Hadamard quantum gate are discussed in details. Mathematical bases and principles of quantum computations are also mentioned. Finally, the role of nuclear magnetic resonance in quantum computations is investigated. Moreover, the extensive list of references is also presented.