|Image source: Google Blog|
1- Storage SettingsGoogle Photos allows you to select your preference for uploading and storing your photos/ videos from these 2 options: High-quality and Original quality. With High-quality option, you have unlimited storage for your photos and videos. With original quality, you consume from your 15 GB default storage. I have discussed them in this post: Are your photos eating into limited storage of your Google account?
2- Auto Back-upYou can upload your photos/ videos from Desktop either (i) in the browser through website photos.google.com, or (ii) using Backup & Sync, a desktop application. Backup & Sync is used by Google Drive and Photos to sync files on Desktop with online storage and you can download it here. On your phone, you can turn auto back-up on or off from Settings -> Backup & Sync.
3- Storage on Google DriveIf you upload your photos or videos directly to Google Drive, they will count against your storage quota (free 15 GB for all Google users) irrespective of their size. They will be uploaded in original quality. For professional requirements like printing banners, you will want to upload your photos as original quality (or to Google Drive).
4- Photos from Drive in Google PhotosIf you have enabled the settings, you can see all your photos and videos stored on Google Drive in Google Photos library. To do so, go to Settings, find: 'Show Google Drive photos & videos in your Photos library', and turn it on. Editing your photos in Google Photos won't modify them in Google Drive. Deleting your photos/ videos either in Drive or Photos will delete them from both places.
5- Photos in Google DriveGoogle Drive, in its left menu, has Google Photos, clicking on which displays your photos/ videos organized by date. You can rename and organize them in folders but that won't create album/s in Photos.
Note: Read more about points 3 and 4 here: How Google Photos works with Google Drive?