Photos made multiple copies of existing photos so that now my storage is full.
Did you sync the photos to your iPhone during a sync with iTunes? Photos cannot be deleted from the iPhone, if you synced them there with iTunes. These photos will be deleted, if you sync again and select an empty folder to sync.
What I want to do is to understand the logic behind iPhone Photos, I want to remove copies of existing photos, and learn how to transfer photos from iPhone Photos to mac Photos.
Photos on the iPhone and the Mac is keeping your photos in a library. This library is a database with many different views of the same photos. The photos are stored only once, but the predefined albums are showing you the photos grouped by different criteria so you can access and find them more quickly.
- The Moments, collections, years are grouping your photos by the location and sort them by date, the oldest first.
- The All Photos album is showing all photos, but sorted by the date you imported them, so you will always find the most recently added photos at the bottom of the album.
- The smart album "Selfies"is showing all photos taken with the front camera.
- The album Panoramic is showing all photos with an extreme aspect ratio.
- The Camera Roll album is showing the photos that have been taken with the iPhone/iPad , transferred with My Photo Stream, or have been saved to the Camera Roll, but not the the photos synced with iTunes.
There are more predefined albums for special purposes. And you can create your own album to group your photos as you wish. Move related albums into a folder, so you can easier find your albums. A photo can be in many albums, but will only be stored once. The albums do not need much extra storage, since they are referencing the photos in the photo library.
To save your photos on your Mac see the options here: Keep your photos safely stored and up to date on all your devices - Apple Support
https://support.apple.com/en-us/HT201313
You can use iCloud Photo Library and sync the devices with iCloud, or connect the iPhone by USB and download the photos to your Photos Library on the Mac. That works best if you are to using iCloud Photo Library.