How to show a hidden element when a user selects an option from a previous element

Question

I'm creating a form for an assignment. How am I able to make a new question appear upon the selection on a value on a different question? For example,

<label for="Etype">*What would you like to enrol in?</label>
<select id="Etype" name="Etype">
    <option value="">Select...</option>
    <option value="Camp">Camp</option>
    <option value="Class">Class</option>
</select>
</fieldset>

and upon the selection of "class" a previously hidden question is revealed beneath the previous question asking "type of class?"

Answer 1

Put this just before your body closing tag:

<script>
document.getElementById('Etype').onchange = function() {
    var isSelected = this.options[this.selectedIndex].value == 'Class';
    document.getElementById('hiddenField').style.display = isSelected ? 'block':'none';
};
</script>

Assuming the hidden element has an ID 'hiddenField':

<div id="hiddenField" style="display:none;">
    Place the hidden field, labels, etc. here
</div>

Answer 2

HTML

<fieldset>
<label for="Etype">*What would you like to enrol in?</label>
       <select id="Etype" onchange="show_hidden(this.value)" name="Etype">
          <option value="">Select...</option>
          <option value="Camp">Camp</option>
          <option value="Class">Class</option>
      </select>

<div id="class">
Type of class : <input type="text" name="class_text" />
</div><!-- #class -->
<div id="camp">
 Type of Camp <input type="text" name="camp_text" />
</div><!-- #camp -->
</fieldset>

CSS

#class, #camp{display:none;}

Javascript

function show_hidden(str)
{
   // if first option was selected, hide both the hidden fields
   if(str == '')
   {
      document.getElementById('class').style.display = 'none';
      document.getElementById('camp').style.display = 'none';
   }
   // if class was selected, show the class fields and hide camp fields if visible
   else if(str == 'Class')
   {
      document.getElementById('class').style.display = 'block';
      document.getElementById('camp').style.display = 'none';
   }
   // if camp was selected, show the camp fields and hide class fields if visible
   else if(str == 'Camp')
   {
      document.getElementById('camp').style.display = 'block';
      document.getElementById('class').style.display = 'none';
   }
}

DEMO