One of the most frequently used constructions in javascript are functions that toggle styles or properties on and off. This can be used for items that require a highlighting effect, or to create layers that expand or contract, or any other property change where you want a property of an element to toggle on and off depending on its current state.

Put this in the head of the document:
 <script>function toggle(id){ 
  var element = document.getElementById(id); 
  element.style.display = (element.style.display == 'block') ? "none" : "block"; 
  } 
 </script> 

Create the trigger for the toggle: 

<a href="javascript:  toggle(myElement);">Open/Close</a>

Create the element you want to toggle open and closed:

 <div  id="myElement" style="display:block"> content goes here </div>