Trying to use user_edit_end hook to get posted form value

I think I need to use this to accomplish the following http://www.solspace.com/docs/detail/user_user_edit_end/

I am using Solspace’s user module and I want to create a notification to the user when their member is moved from pending to another group.

I know the user module does that already, but it is a broad solution and I want some more customization than that.

What I want to do is:

I am creating a mini Control panel, so the admin I assign to this mini cp can update the pending member’s to their appropriate groups. Once the user is assigned to anything other than pending, then send an email to that user saying they are now approved.

The form is setup as

{exp:user:edit 
  form:id="member_form"
  form:class="register-alumni"
  member_id="{segment_3}" 
  allowed_groups = "4|24|23"
}
  <h3>{screen_name}</h3>
  Select graduation year to confirm their account: 
  <select name="group_id">
  {exp:query sql="SELECT group_id AS gid, group_title FROM exp_member_groups WHERE group_id = '4' OR group_id ='24' or group_id = '23'"}
    <option value="{gid}" {if group_id == gid}selected="selected"{/if}>{group_title}</option>
  {/exp:query}
  </select>
  
    <input type="submit" value="submit" name="submit"></p>
{/exp:user:edit}

I tried doing this

<?php $_GET['group_id']; ?>

but the security settings unset data, so I can not get the data from get/post, so that is where I think I will need to use this hook http://www.solspace.com/docs/detail/user_user_edit_end/

I have never used a hook before and I tried creating my own extension. I am lost on how I would use the hook with the extension as well as getting the data from the hook to use for my conditional and processing the email notification function.

I read this http://expressionengine.com/docs/development/extensions.html and I feel I am missing the part about how to obtain the data from that hook.

Any help is appreciated.

This is for v1.6.8