That depends...
1. Do you want to create a new product page with a photo, description, etc?
OR
2. Do you want to create a page that you can link to from anywhere in your site?
Answer1: If you want to add a product to your site, go to inventory/product editor - then click the link that says add a new product.
From there, you can tinker with different aspects of the product. If you want to add custom html for your product description; click the "html" check box next the WYSIWYG button. Next, copy and past your html into the list box.
Note you'll have to change the path names to photos in your html. The path would be somthing like this images/products/..../.......file extension.
Warning: If you add your html then view it in the WYSIWYG editor, all path names to your pictures will change to
http://www.yourdomain.com/etc/etc ***You do not want to leave it this way**** Make sure the paths read images/products/etc/etc.file
Answer2:If you want to create a page that can be linked to from anywhere in your site, go to: site HTML/custom pages - then add your page. Again, you can copy and past your html into the list box. Each custom page you create will be assigned a url. Use that url in your html for links, etc.
I hope this helps. Enjoy!