Downsizing gears towards nanoscale has opened the possibility to realize nanoscale mechanical machines, which is of great interest in the area of nanorobotics and devices immune to radiation. In this area, there are several crucial issues, such as how to trigger single gear rotation, the ability for interlocked rotation of many gears, and frictional properties during gear rotation on the surface. Here, we are aiming at addressing these three fundamental questions. First, we propose the rotational version of the Anderson-Holstein model within the nonequilibrium Green's function formalism as a possible phenomenological description of single gear rotation by switching between two potential energy surfaces of the highest occupied molecular orbital and lowest unoccupied molecular orbital. Secondly, we exploit the nearly rigid-body approximation for extracting the collective rotational variables of given molecule gears. The analysis of the probability distribution in thermal equilibrium for those variables between two coupled molecular gears has been studied with classical molecular dynamics simulations. This allows us to estimate the interaction potential profile between gears, which is strongly depending on the gear separation distance. Furthermore, we propose a method called locking coefficient diagram to characterize the ability of gear collective rotations under external torque. In comparison, a similar analysis for the case of solid-state gears is also studied, which shows a very robust mechanical transmission behavior. Hence, we have designed a two-digit mechanical pascaline based on these gears, which are feasible for carrying out simple calculations. Finally, the rotational friction for solid-state gears on top of a surface is also studied within classical molecular dynamics simulation. We find a regime of viscous dissipation, which is purely arising from the van-der-Waals interactions. Furthermore, the friction is closely related to the available degrees of freedom in the substrate. By analyzing the velocity distribution for the atoms in the substrate, we find that the rotational dissipation mechanism is largely related to surface phonon excitations. We expect that the results of this thesis will provide some insight for future studies in the area of nanoscale mechanical machines.