window.onload = function() {
    // all your stuff that should execute on page load underneath here
    write_added_text(); // functions returns nothing, only doing it's own stuff



    // another example
    document.write(get_added_text()); // get_added_text will return something
}

function write_added_text() {
    var a = "Hello";
    var b = "World";
    var merged_text = a + b;
    document.write(merged_text);
    // no return here, therefore document.write(write_added_text) wont do much as document.write wont get any string to write
}


//function underneath here is an example of returning values

function get_added_text() {
    var a = "Fuck";
    var b = "HAHA HE SAID FUCK, HOMODICK";
    return a + b; // we dont need to make another variable to return our desired end result. just returning is like this will work as well
}