best time for whey protein shake

Is it better to drink whey protein shake for breakfast or after my workout?? I workout before dinner. My workouts consists of 40 mts circuit training 4X wk and i just started 30 mt walk/jog intervals 3X wk. After my workout, i usually eat spoon peanut butter to hold me until dinner is ready. Also, does protein shake help more in losing weight? sorry for the weird questions, im new to all this fitness and lifestyle change. thank you in advance!