Renormalization Group Equations (RGEs) are indispensable tool to know the behavior of physical parameters at different energy scales. They are also extremely crucial if we want to extend our known Standard Model gauge group by some extra gauge groups and the $\beta$-functions are the soul of these RGEs. In literature although it is quite common to find long, final expressions of the RGEs, unfortunately it is difficult to find any pedagogical review to calculate these $\beta$-function coefficients explicitly from the known formulae. Therefore in this note we shall try to explain the detail calculations of RGEs by giving some explicit examples taken from the literature. The goal and hope is to provide a hand on experience on calculating these RGEs for the young readers.