Im planning to create a chat client/server for a website. The client is easy, i think. The Problem is with the server, i dont know how to execute the server on my webhost. Does anybody had an experiance with this? Does the server need to be in .jar format? What do my webhost need to run this java server?

If you have a Java application that you want to run on your server, there are a number of things that your webhost will need to provide you. First, the JRE (Java Runtime Environment) needs to be loaded on the server. Often this takes the form of Tomcat or some other lightweight JSP/Servlet container. Second, you must have permission to do so -- I would say that your best bet would be to talk with your webhost as most (not all) everyday hosts don't allow Java functionality due to encapsulation, overhead and security concerns.