Can't load music onto my iPhone 5S with my Mac running 10.6.8
There are 2 options for putting music on your iPhone. Manually or Syncing. If syncing is enabled then there's a Music-Section when your iPhone is selected, where you can check playlists, artists etc. that you'd like to sync. Alternatively there's a checkmark that says "Manage Music manually" (or something alike - my system is german). When you can put music on your iPod/iPhone via drag and drop.