How do I delete photos from my MacBook Pro?

Do you want to delete photos from your Photos library, the entire library or the Photos app?

If it's photos from your Photos library here's how:

Deleting Photos from a Photos Library

1 - regardless of where you are in the library, i.e. Photos, Memories, Favorites, People, Recents, Imports, albums or smart albums, select the photo(s) you want to delete and use the key combination of Command+Delete to move the photos to the Recently Deleted smart album.    Without the Command key held down you'll be presented with a confirmation Yes/No window regarding the deletion. 

2 - click on the Recently Deleted smart albums in the sidebar.

NOTE 1: If you're using Photos 1.2 or earlier use the File  ➙ Show Recently Deleted menu option.

3 - in the Recently Deleted album you can opt to let the photo automatically delete after the 30 day waiting period is up, delete them immediately or restore them to the library.

NOTE 2: deleting a photo from an album, slideshow, book, etc., with the Delete key only deletes the photo from that item. There is no key combination that will delete a photo from a project and move it directly to the Recently Deleted smart album.

NOTE 3: deleting a photo from a Moment or Collection (the Photos window) or the All Photos window deletes ALL occurences of that photo in the library.

NOTE: remember what Tony said about iCloud Library!

Assuming they are in the photos library - select them in the all photos view, and go to image>delete (or just hit the delete key)

BUT be aware that if you are using iCloud to sync your photos, anything you delete on your Mac will be deleted on all your devices. You will lose them.