Question: how do i download my music from my mac to my iphone?
Answer: Connect your device to your Mac. ... 
In the Finder on your Mac, select the device in the Finder sidebar.
Select Music in the button bar.
Select the “Sync music onto [device name]” checkbox to turn on syncing of your music. ... 
To sync a selection of music, click “Selected playlist, artists, albums, and genres.”