What Will happen if I sync my music on my Iphone?

I got an IPhone 4 for my birthday, and I don't want to lose my apps or my contacts or any picture. But it won't let me put music on. And when I go to my Music it says Sync and is all gray. So i hit the box and select "Selected playlist, albums, artist, and genres" and then i hit "Apply" then it comes up with "Earsing and Syncing replaces the contents of this Iphone with the contents of this Itunes library" Will my Apps, Contacts, ect. Get deleted if i hit "Erase and Sync"?

You have to add the music you want into the iTunes on the computer you originally set up your iPhone on.
If you try to do it on another computer then that message pops up.

Instead of syncing, click "manually manage music and video" in iTunes and then drag and drop the music.

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