Hi,
First, make sure that you're not just wasting your time. There are untold numbers of open-source help-desk applications already available, and of course dozens of excellent commercial products also. If you're doing this for a job, then do consider what's already available. If you're doing this for fun, then consider whether there might not be a better way to spend your time.
But if you do decide, for whatever reason, to continue, then the first thing you probably want to do is sketch out some requirements. If you have a customer, work with them to do it. If this is just for fun, then you'll have to do this yourself. Think of what you want your system to do, and write it down. Make a prioritized list of those features, and then get ready to attack the first one!
If you do continue with this, and you develop that requirements document, then you can certainly come back and say "My first goal in building this system is X, how do I do that?" and I'm sure you'll get some help here at the Ranch.
One more thing: you probably want to have a look at
this document that explains how to get the most out of the Big Moose Saloon.