Declaration (prototype) for void function

I'm having trouble understanding what I'm supposed to do and how to do it, please help

Code:

#include<iostream>
#include<fstream>
#include<string>
using namespace std;


/*  TODO:   Write the declaration (prototype) for void function GetLeast that
            takes an ifstream parameter called infile as an input parameter
            that is changed, and that has an int parameter called lowest
            that returns a value.


            Document the data flow for the parameters with appropriate comments.
*/


//------------------------------------------------------------------------------


int main()
{
    int smallestValue = INT_MAX;        // Initialize smallest to maximum range
    ifstream dataFile;                                  // File input stream
    const string filename = "data.txt";                 // Input file name


    cout << "Opening file...";


    dataFile.open(filename.c_str());                    // Open file


    if(dataFile)                                        // File opened OK?
    {
        cout << "file opened." << endl
             << "Begin searching for lowest value...";


        /*  TODO:   Call function GetLeast, passing the ifstream variable
                    and int variable as arguments.
        */
        






        cout << "done.\n" << endl;                      // Print result


        cout << "The lowest value found was "
             << smallestValue << endl;
    }
    else                                                // Problem opening file
    {
        cout << "could not find or open file: " << filename
             << endl;
    }


    dataFile.close();


    cout << "\nEnd Program.\n"
         << endl;


    return 0;
}

I suppose we can start with this, and see what you can come up with for the implementation and explanation.

Code:

void getLeast ( ifstream &dataFile, int &smallestValue );

The following tutorial might help you. Take a look at it and see what you can do. Don't worry if you can't get it to copmile or work, just have a go and post your best effort.
Functions in C and C++ - Cprogramming.com