how to transfer files from macbook air to i phone 5s

You may want to reply with more information about what you are wanting to do, but the following possibilities come to mind:

AirDrop (if your MacBook Air is a 2012 or later model and has Yosemite installed). Use AirDrop to send files from your Mac to another nearby Mac or iOS device - Apple Support

iCloud: https://www.apple.com/icloud/icloud-drive/

3rd party solutions such as Dropbox, OneDrive etc.