Go into the settings/preferences, and go into “Advanced”. You’ll see two check boxes there. One that will rename your files according to how iTunes likes it, and the other that will copy them. Uncheck them both.
You can change your iTunes Media folder location to your hard drive, import all your music in from let’s say your laptop, and then organize it all with iTunes, but I found that to be a lot of trouble. Just uncheck the two and go about things as you see fit.