Why won't iTunes let me drag individual songs onto my iPhone?

I have the new itunes (11) and it won't let drag individual songs onto my iPhone. I tried looking it up on the internet, and one person said "make sure that your iPhone is setup to sync your songs manually instead of syncing only the checked songs/videos." What does that mean? I don't want all of my library on my iphone… Please Help!

Every time you sync your iPhone, you must sync everything you want. So if you want to sync just one song in there, you must sync that song plus what you already have in there. Otherwise iTunes will simply sync that one song in there and nothing else. To manually determine which albums (or artists) you want synced into your iPhone, simply open iTunes, then connect your iPhone to your computer via the supplied USB cable. Then access your iPhone via iTunes. Go to the "music" tab of your iPhone in iTunes. Then check "Synchronize music", then check "Selected playlists, artists, albums and genres". Then simply scroll down and only check the albums you want to have in your iPhone. This way, you can avoid syncing everything you have in iTunes to your iPhone.

Hes right, the iPhone device page, where you see the Summary, Apps and other stuff? There's a Music tab there between Apps and Movies, go to that page and uncheck the "Sync Music" checkbox at the top.

I usually have that unchecked, but just experimented with Checking it, I could not drag songs onto the device manually after trying it, uncheck and hit the "Apply" button at the bottom.

EDIT: MISSED ONE THING! On the Summary page of your iPhone on iTunes. The Options area has this checkbox: "Manually manage music and videos", make sure that is Checked, don't forget to hit "Apply".