Vector with unsigned int

My teacher assigned this question for me, where i have to create a code for fibonacci, i know how to make a fibonacci, but i can't really see what am i going to do with this code that he gave and said that it has to be on my code.

Can anyone make a code that satisfy this? I'm really trying to understand, but i've tried googleing it, watching some yt tutorials, but couldnt understand what is this supose to do.

    #include "function.h"
    
    std::vector<unsigned int> fib_below_n( unsigned int n )
    {
        // ALL: add your code here
    
        // ALL: This is just a STUB. Change the RETURN for what you judge right.
        return std::vector<unsigned int>{};
    }