How to show pages with PHP code

I jus installed a WP copy in my server to manage a news webpage.

I also wanted to add some non-dinamic information to my website. I could manage almost the all contents with the Pages tool, but I couldn’t use a script that I wrote in PHP to show the IP adress of the visitor. How can I do it? I tried a plugin to show PHP code in posts, but it doesn’t help me.

I also wanted to organize my Pages in categories, but the option to put one inside another doesn’t help me neither. What can I do?

Thank you very much and sorry for my English, but I’m still an English student from Spain.