I'm always looking for the easy way to implement code. Here's a real easy way to produce a message box on a web page;

<script type="text/javascript">
alert("your message here")
</script>

Kudos to http://www.xulplanet.com/tutorials/xulqa/q_msgbox.html!
The above site expands on the code to include capturing return information, confirmation dialogues and more.

Really simple code to return a user to the previous page in a browser.

There are multiple ways of implementing the code;

1) In-line;

<script type="text/javascript">
history.back()
</script>

2) As a link;

<a href="javascript:history.back()">Back</a>

3) As a button; Sorry no demo code for this method. Embedding "javascript:history.back()" in an OnClick event should do the trick. I haven't tried myself, yet.

 

Props to http://www.cryer.co.uk for posting sample code.