How to order objects... puzzled on the last function I somehow copied and ...

friends = {
ariane : {firstName: "Ariane",
         lastName: "Bertram",
         number: "696966123",
         address: ["via bellezza 37", "Brasile", "53550"]},
       
bill : {firstName: "Bill",
       lastName: "Porte",
       number: "666 666666",
      address: ["ta dah", "palle", "99"]},

steve : {firstName: "Steve",
        lastName: "Dell'inferno",
        number: "213456987",
        address:["Oppa", "Gang nam", "57173"]}
};

var list = function (){
for (var names in friends){
console.log(names); }};

var search = function (name){
     for (var contact in friends){
        if (friends[contact].firstName===name){
             console.log(friends[contact]);
             return (friends[contact]);}}};

       
//In this exercise I quite didn't understand the function for/in, and the last part where 'friends[contact].firstName ... does it mean contact is in friends and start with firstName and I have to make it equal to name because I can give it the property of a function?!