When to use function expression and when to use function declaration

Question

Here i have two questions regarding javascript functions

1. When to use function declaration and when to use function expression

2. This is an function expression

   var run = function (){ // code stuff }

This is an function declaration

function walk(){
// code stuff
}

What do we call functions written inside below object(human) is it declaration or expression?

var human = {

  think : function(){

       }

 roll : function(){

     }

 }