Do one of the following:
Drag the selected photos to an album in the sidebar, or Control-click a selected photo and choose Add To > [album name].
Control-click one of the selected photos and choose Add To > [album name].
Drag the thumbnail in the selection indicator at the top of the window to an album in the sidebar.
Control-click the album, choose Delete Album, then click Delete.
The album is removed from the library and from Change preferences in Photos on Mac