Photos and All Photos are two differnt ways to access the library.
- "All Photos" is a smart album, showing you all your photos, even the photos you have hidden. It is sorted by the date you import the photos, so the most recently imported photos will always be at the bottom of the list.
- "Photos" is the library view. It is sorted by the capture date and split into moments. The moments are created automatically based on the capture date and the location. Photos taken at the same time at the same place appear in one moment. Related moments will be grouped into collections. And collections into years. Clicking the places names in the Photos view will show the photos on a map. To switch between moments, collections, years in the Photos view use the < > keys to the right of the traffic light buttons.
- See this help page: https://help.apple.com/photos/mac/1.0/?lang=en#/pht56eafa987