The Photos app gives you instant access to all your photos and videos associated with any Google Account set up on your phone.
To open it, touch 
Photos.
To open Photos:
Camera app
Swipe from right to left
All apps screen
Touch Photos
When you’re signed into your device with your Google Account, the Photos app makes it easy to auto-backup all the photos and videos you take, organize them, and share with friends.
You can also browse, search, crop, edit, and tag photos, and create albums and movies.
Touch 
Menu to:
Switch to or from Google+
Organise and edit your photos and videos
Create and browse albums
Explore Auto Awesome animation, panoramas, or merged group shots created for you automatically
Browse photos of yourself