You have a website. Now the first step is to find out, what "engine" - that is what webserver is hosted on the webserver.
Most common webserver (especially on "free hoster" webserver) is apache - therefore you mainly may be able to run applications that are written in the php language.
For running jforum your webserver requires some webserver like jboss, tomcat, jrun, ... the most common there for java engines may be tomcat. But there is like almost no free webhoster providing access to server like these.
If you wish to configure your application to run on a certain domain/port, you can use the systemglobals.conf in the end, once you know that the server can interprete java
Aside that, you do not have to understand java nor tomcat ;) Only know if the required server is installed on the webserver :-)
If you cant find out manually .. write an email to your hoster and ask.
[originally posted on jforum.net by Sid]