You can find where your iTunes songs are stored on your hard drive by first going to your Users folder (inside your hard drive folder). Double-click on your user folder and then again on the Music folder. Inside the Music folder there should be a folder named iTunes. Double-click on the iTunes folder and then again on the folder named iTunes Music (or iTunes Media). Your songs should be organized by artist within that folder (if you have "Keep iTunes Media folder organized checked within iTunes > Preferences > Advanced).
If you can't find that folder or don't see any music in it, open up iTunes and go to iTunes > Preferences > Advanced and make sure the option "Copy files to iTunes Media folder when adding to library" is checked.