
Once you've migrated your image library from iPhotos or Aperture (or both), you'll probably want to add all the images from your iPhone or iPad and get everything organized so you can quickly find pictures from specific dates and events in the future.
To help you accomplish both of these tasks, we've written up a tutorial that provides an overview of how to import pictures into the Photos app on OS X Yosemite and gives a few suggestions for how to organize your collection.

Connect your device (iPhone, iPad, or digital camera) to your computer using the USB connector and open the Photos for OS X app.
Select "Import" from the list of tabs at the top of the screen in the app.
Select the images you wish to add to the Photos app, or select "Import All New Items" to add everything from your device.
Imported images will automatically be added to the "Last Import" album in Photos. You can see your photos using a number of different views, including the main Photos tab, which displays all pictures that you have added to the app and any pictures that you have taken using an iOS device that is connected using My Photo Stream.
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Article Link: How to Add and Organize Images in Photos for OS X Yosemite