Separate a single list into a truthy and a falsy lists [duplicate]

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I am doing a course and it asks me to, "create a function that accepts a list and a callback function that returns a list of truthy values and another list of falsey values."

The answer I submitted was:

def partition(lst):

    truthy_list = []
    falsy_list = []
    for i in lst:
        if i in lst == bool(lst):
            truthy_list.append(i)
        else:
            falsy_list.append(i)
    return truthy_list
    return falsy_list

The answer given by the instructor is:

def partition(lst, **fn**):

    trues = []
    falses = []
    for val in lst:
        if **fn(val)**:
            trues.append(val)
        else:
            falses.append(val)
    return [trues, falses]

It looks like everything is the same except the second part in the function defined "fn" and in the if statement. I am at a loss on what that second part is in the function and what the if statement is calling out. If someone can take me under their wing and explain to me what I am not understanding on this and what that fn(val) is calling out it would be much appreciated.