Organise Photos into Sections.

You can organise them in folders and albums if you wish. Note that a folder must hold an album to put pictures into (a folder cant hold pictures directly)

see:

https://appleinsider.com/articles/21/08/22/how-to-manage-album-collections-in-photos-for-macos

Placing a photo in an Album does not make a copy of the photo. You can place a photo in no albums or in one album or in many albums. Whichever of these you do, the Library contains precisely 1 copy of the photo.

Welcome, glad to help.

To add to Dandelion's advice:

Do not delete items from the Library, unless you want to remove them completely from Photos.