Download a copy of Mach3 and play with it. Since you're not connecting to any machine, you don't need to address any of the issues about parallel port, or 32/64 bit, laptops or anything. Watch the tutorial videos and read the manual. All of this will be free.
Since you already know some manual machining, you should be able to get a good feel for how g-code works, and how the machine is controlled - referencing systems, quite a lot.
Your machines at work may have different systems than mach-3, but you'll hopefully be in a better postition, knowing what to expect and looking for it, than not knowing at all.