Why does this not work?

I am going through the python Code Challenge: Functions where it asks:

"Make a function named add_list that takes a list. The function should then add all of the items in the list together and return the total. Assume the list contains only numbers. You'll probably want to use a for loop. You will not need to use input()."

I got a bit stumped and found the right answer(s), but I am wondering why my code doesn't work for the first part:

#add_list takes a list
def add_list(list):
   #num breaks it up into pieces
   for num in list:
   #add becomes the sum of the pieces
   add = sum(num)
   #returns the summation
   return add

A google search suggested that I need an iterable term to use sum. Perhaps that's the part I'm not quite understanding? Does sum need a list, not the pieces fed by a for-loop? Something more like:

def add_list(list):
   add = sum(list)
   return add

Thanks for any answers, so far learning code is a ton of fun!