I'm trying to create a multiplayer game on yur browser. And I need to send messages from server to all clients every few seconds. I have no idea how can I run a script on server side? Sorry, I'm a complete newbie :) Thanks!
You didn't specify what is your server technology. If you have no choice yet, go for node.js (and express) as your server technology and use socket.io for real time messaging. Have a look in the Getting Started section. They have a chat demo and a collaborative white board demo which are in a way similar to what you are trying to achieve.