Help about PHP and JScript

I need a HUGE help, because I am new to PHP and do not have much experience.

I need help regarding PHP and JScript, iframe
I have a page with html and iframe
navigation links are on the side and top, and everything opens in the iframe to the right side of navigation.
HTML: KOMPAS - Bike Shop
And it works almost OK
I do not know why the thumbnail viewer displays the image only within the iframe?

For sidenav I used stu nicholls dot com | menu - Tree Frog Slide

and for thumbnail viewer Dynamic Drive DHTML Scripts- Image Thumbnail Viewer

but I tried to make the entire page in PHP, and now it works almost well
but I want sidenav to works as in the example with html

I want Sub level to remain open until I click on top level
example with PHP
PHP: KOMPAS - Bike Shop

How to make that sidenav works as in the example with HTML
I want to change contents only inside “Maincontent” div?

I apologize for the bad english but I’m not the worst
Chick Point

If someone needs to send the original PHP code

Thank you for reading this especially if you are able to help me out on this.