The Music tab gives you a number of options for controlling what music is synced to your iPhone and how.
- Sync Music - You must check this in order to sync music to your iPhone.
- Entire Music Library does exactly what it sounds like it should: syncs all your iTunes music to your iPhone. This only works if your phone's storage is bigger than your library, of course. If not, you'll get some, but not all, of your music.
- Selected playlists, artists, albums, and genres lets you decide what music gets downloaded to your iPhone.
- If you select this, iTunes downloads only selected music to your iPhone. Sync playlists by checking the boxes on the left or all music by particular artists by checking the boxes on the right. Sync all music in a particular genre, or from a given album, by clicking the boxes at the bottom.
- Include music videos syncs them to your iPhone if you have any.
- Include voice memos syncs voice recordings to/from your iPhone.
- Automatically fill free space with songs fills unused storage on your iPhone with music that you haven't already told iTunes to sync.