Syncing your photo library means that all of your devices will display the same photos within the Photos app, no matter which device was used to take the pictures.
With iCloud Photos, every photo and video you take is automatically uploaded to your iCloud Photo Library, and then synced (transferred) to all of your other iCloud-enabled devices. You may already be familiar with iCloud if you use it to back up your iPhone’s data. ICloud is Apple’s cloud-based storage facility that allows you to store your files remotely and access them from a variety of devices via Wi-Fi. In this tutorial you’ll learn how to set up and use iCloud Photos, so that you’ll have access to all of your photos on all of your devices. With iCloud Photos you’ll always have access to your entire and most recent iCloud Photo Library collection, no matter where you are or which device you’re using. iCloud Photos works with iPhone, iPad, iPod touch, Mac, and even Windows computers. Apple’s iCloud Photos feature allows you to seamlessly sync and store your photos and videos across all of your devices.