Jquery: how to show additional text when a user clicks into a form field

I am new to Jquery and am trying to find a way to show additional text when a user clicks into a form.

The input field looks like this: <input class="fee开发者_开发百科d" id="post_title" name="post[title]" size="100" rows="20" type="text class="title_search""> and the the rest of the text is contained with a <div class = "post-input">

Any help pointing me in the right direction would be much appreciated :)

    $('input').focusin(function() {
       $('div').show();
    });

    // Hide the text once you are out of the input
    $('input').focusout(function() {
       $('div').hide();
    });

This is the basic idea. http://api.jquery.com/focusin/

$('#post_title').click(function(){
  $(this).next('.post-input').html('hey! you clicked the input!');
});

//asuming the div is next to the input, if not i suggest placing an id to it, too.

and if there was alredy text in the div and you just want to show it

$('#post_title').click(function(){
      $(this).next('.post-input').show();
    });

$('.feed').click(function() {
    $('.post-input').show();
}