transferring music from my MacBook Air to my I phone

See here: link-> Sync your iPhone, iPad, or iPod using your computer - Apple Support

Learn how to sync music, movies, and more using your Mac or PC.

would help if you detailed the model of computer. I'll assume you use the Music app on the Mac. Then add you music to the library and create playlists then sync playlists to iPhone. I'm assuming you have music on your Mac from owned music cds.