Change Inner Content Of The Second Child Node

I'm beginner, and there is a task in exam to change inner content of the second child node. Can't get,maybe link to an article how to do it, because I can't find anything in my study book;:mad: edit: is this correct?

function SetUpTranslation() {
var phrases = document.getElementsByTagName('p');
for (var i=0; i < p.attributes.length; i++){
phrases.secondNode.innerHTML=french[i];
element.onclick=swapFE(phrases.secondNode);
element.onmouseup=swapFE(phrases.secondNode);
}
}