I've got my application working, but I only know how to access it at http://localhost:8080/LogIn/log_in.jsp ...
How do I get this online??? I have a current web site not using tomcat, so I was hoping I could make a link on a current page to my log_in.jsp page with tomcat... but if I can't do that, how do I get my app online in general? How can I access the site from a different computer?

This is a little beyond the scope of a JSP book. But to run Tomcat in an internet connected system you will need to have a globally addressable IP address and it's helpful if you have a domain name.

The 'localhost' is a "special" hostname which references the loopback address (127.0.0.1) of your network stack and is equivalent to the local machine.

To get your web application working online you will need to find an ISP that will support hosting web applications (it doesn't have to be Tomcat, that's the beauty of web applications).

OK - if anyone actually gets something working from this book's FINE examples...
I found a host that supports a private JVM and Tomcat. The host is dailyrazor. check it out if you get that far - and good luck everyone!