Molecular conductivity is the ability of a molecule conducting electrons on a single molecular level.While recent advancements on instrumentations enabled direct measurements for molecular conductance, it is also of great significance to predict and understand how the current flows through molecular systems, especially single molecules, which could potentially enhance the understanding their charge transport properties. In this worksheet, we will explore the microscopic origin of molecular conductance and current-constraint two-electron reduced density matrix theory in preparation for modeling the molecular conductance.