Since the synchronous Buck converter is a switching regulator, the switching elements, Q1 and Q2, alternate turning on and off during each switching cycle. In the first part of the switching cycle, Q1 turns on while Q2 turns off. The direction of current flow in this configuration is shown as red arrows in the picture here. During this time when Q1 is on, the current is being supplied to the output load from the input through the inductor. As the inductor current is increasing, energy is being stored in the inductor. The output capacitor is also being charged by the current, so energy is stored there as well.