What are the differences between the effects of a catalyst vs reactant concentration on the position of equilibrium/ why?

An increased concentration of reactant will shift equilibrium to the right, because the reactants will react to form more product in order to decrease concentration again. However, while a catalyst will increase the rate at which equilibrium is reached, it has no effect on the position of equilibrium - it does not alter the final concentrations of reactant or product, only the time at which these are reached.