I'm a retard

Preface: I'm fuck awful at scripting

Making a little self-interest site to pass the time and I'm stuck when trying to create a script that will allow 2 individual buttons labeled "Previous" and "Next Page" from doing their respective jobs, which I would assume is obvious.

Could anyone inform me, or direct me to where I may learn to implement such a feature? Also, keep in mind my preface and cut me some slack if you try to explain the function yourself.

Appreciated

What's wrong with this code

<script type="text/javascript">
var pNum=0;
var maxPage=100;
function next()
{
pNum++;
if (pNum > maxPage) pNum=0;
document.getElementById("frame").src="page"+pNum+".htm";
{
</script>

Whenever I go past the max number of pages it goes to a 404 instead of cycling back to the start page.

What do?