BEFORE you upgrade your computer operating system to 10.10.3 - update your iPhoto to 9.6.1. iPhoto 9.6 or earlier is not compatible with the current version of Yosemite (10.10.3). After updating to the current version of Yosemite you’ll see Photos (not iPhoto) on your dock. Photos is Apples new photo applications and is replacing iPhoto; when you launch Photos you’ll be prompted to migrate your iPhoto library to the new Photos.
The migration might take a while, depending on the number of pictures you have. Photos will migrate all your pictures, albums, slideshows etc. The only concern you might have is available space on your hard drive as after the migration you’ll have both an iPhoto and Photo library. Once the migration is complete you can delete the iPhoto library - freeing up the space.
This course will help you decide whether to transition to Photos right away, walks you through importing photo libraries from iPhoto and Aperture, explains the Photos interface and how you can organize your images, gets you going with the editing tools, and assists you with copying photos to iOS devices and Apple TVs. It also shows you how to create books, cards, calendars, and slideshows.
Particularly helpful is the explanation of how Photos works with iCloud, including using iCloud Photo Library to create a centralized photo library for all your devices and sharing photos with friends and family via iCloud Photo Sharing. While we now think it’s safe to turn on iCloud Photo Library, beware that it may overwhelm your Internet connection.