What are: WAR files, build.xml, etc?

[ja...@spunkysoftware.com]

I haven't been able to find out how to make a WAR file or what it's for, or
how to write a build.xml file, or anything like that in the Tomcat docs.

I have ant installed, I know build.xml has something to do with ant.

Also, I modified a Bean in the /examples directory that comes with Tomcat,
modified the .jsp file, recompiled the Bean but I got an error, with an
incorrect line number. I couldn't understand what the error was, there was
no error in my Bean. I just added two new methods and exercised them in the
.jsp file, or I tried to anyway. The Bean compiled without a hitch, but
Tomcat wouldn't execute the JSP file. What's going on? Is there something
I'm missing?

Does this mean I can't just add JSP files, servlets and beans anywhere and
start using them? If not, why not? What do I have to do? How do I build an
application for Tomcat? I haven't seen anything in the documentation that
tells me how to do this.

Thanks heaps.
James