Starting with OS X Yosemite v10.10.3, your Mac includes the Photos app. If you were using iPhoto before updating, you can upgrade it to Photos for Mac. When you install OS X Yosemite v10.10.3 or later, Photos is part of the update. In many cases, if you had a single iPhoto library in your Pictures folder, your entire library — including your photos, videos, projects, albums, and so on — automatically appears in Photos the first time you open it.
Photos store your library in the Pictures folder on your Mac. When you upgrade an iPhoto library, your Photos library will be stored in the same location as the original library. Nothing will change in terms of location. Photos uses the same master file as iPhoto, so you do not need the double space to run the apps. Photos turns iPhoto Events into albums, which you’ll find in a folder called iPhoto Events in the Albums view. Some metadata, like star ratings and flags, will be transformed into keywords, so you can easily search for them. Learn more about how Photos handles Smart Albums and content and metadata from iPhoto.