Help with PHP - How to?

[Ladybug]

Hi, I'm trying to put a .php shopping cart into a webpage and I really can't figure out how to use .PHP in a placeholder. Is this possible? I'm not sure where to put the shopping cart files - what path to use. Both the Web Designer site and the shopping cart uses index.php and they seem to be conflicting with one another even though they are in different folders.

I have the index.php in a folder and within that folder is a folder with the files for the WD website files and also another folder named shop with the shop files and folders within that. I'm sure I'm doing it wrong and wondered if anyone knew how or if I can get this accomplished.

I put a pic of how I have the folders.

I hope this made sense.

Thanks,
Ladybug