Buck converter calculations
The ESR value of your capacitor and inductor affect the ripple output voltage. The output ripple voltage can be estimated based on the inductor ripple current (delta IL) and the ESR of your capacitor.
The inductor shall be used to reduce the ripple current (delta IL).
delta IL = (1/F*L)Vout(1-Vout/Vin). Where F is the switching frequency.  In the same time the capacitor is selected with the following calculation: C=Ip/(F*Vripple); where Ip is the peak output current and F your switching frequency. The Ripple voltage is based on requirements and performance expectation.