translating lambda in function

[fabs]

hello everyone,

i am a python beginner and would like to understand a bit more about lambda, how to "read" it and when to use it instead of functions. I am working with a list of points (x,y,z) and using this block of code to sort the list based on the z value:

orglst.sort(key=lambda orglst:(orglst.Z,orglst.X,orglst.Y))

now, this code works well. It was written by someone else and I cant really understand it because I am not familiar with lambda. I then tried to replace the lambda with a function, so I go a way I am familiar with, but it didnt work. In my mind, I was writing exactly the same instructions:

def reorder(list):
    return: list.Z,list.X,list.Y

orglst.sort(key=reorder(orglst))

then I tried something else, that also went wrong...

newlist = []
for point in orglst:
    newlist.append(point.Z)

sort.orglst(key=newlist)

Question 1: why are my alternatives not working?
Question 2: why would I use lambda instead of a function anyway?

Cheers!