How can I autofill my iPhone with music from iTunes?

You can fill up a portion or all of the empty storage space on your iPhone with songs from your iTunes library automatically. Here's how to use the autofill feature:

1. Make sure your iPhone is connected to the computer and iTunes is running.
2. On the Summary tab of the iPhone, make sure the box next to "Manually manage music and video" is checked. Click Apply. This step will not remove music already synced to your iPhone.
3. On the left side menu under DEVICES, click the arrow to the left of the iPhone to expand the iPhone contents.
4. Select Music from the expanded iPhone menu.
5. At the bottom left of the iTunes window you'll see options for selecting the source of autofill songs. On the right there's a button labeled Settings.
6. Choose the source from the pull-down menu. Click Settings to allocate storage space and decide how songs are selected.
7. Click Autofill and the iPhone will sync, filling up space with music automatically.