Adding photos to an album in Photos?

I am failing massively with the drunk 'logic' of how Photos is supposed to work, after using normal, more 'sober' Apple apps. But… I cannot add a photo to an album! In any Mac app, iPhoto, iTunes, Apple Mail etc., one can drag an item to an album, playlist, or message folder. Despite the demo video saying I can 'choose' what to add to the sidebar, I cannot. Dragging a photo does NOT add it to an album in Photos. It does precisely… nothing.

I'll add a operate question, but if anyone has recommended alternative photo library managers, I'm really interested in what people are using to replace Aperture and iPhoto. I am founding nothing but faults with Photos (the glaring white background that cannot be changed, being pretty major, and no easy way to see basic things like filenames). I'm keen on a working alternative.