1. The "back" button
 1.1. As a text
 <a href="javascript:history.back(1);">Back</a>
 
 1.2 As a submit button
 <input type="button" onClick="javascript:history.back(1);" value="Back">

the code:
javascript:history.back(1)

javascript: = define that we will use javascript for the next lines
history.back = define that we are using a history function, based on past sites
(1) = will back 1 site only. 

1. The "next" button
 1.1. As a text
 <a href="javascript:history.go(1);">Next</a>
 
 1.2 As a submit button
 <input type="button" onClick="javascript:history.go(1);" value="Next">
 
the code:
It's almost the same of back.

javascript:history.go(1)
 
javascript: = define that we will use javascript for the next lines
history.go = define that we are using a history function, based on first sites
(1) = will advance 1 site only. 
 
 
Very simple no? Now you can make the navigation of your site more useful.