How do highlights and hidden photos work?
Highlights open the gallery with your favourite frames; hidden photos stay in the gallery, out of sight.
Highlights
In a photo's ⋯ menu, choose Add to highlights. For several, select them and press Add to highlights in the bar.
The gallery gets a Highlights tab, first in its row of tabs, with just those photos.
Remove from highlights takes a photo out again.
Hidden photos
Choose Hide from the gallery in the photo's ⋯ menu, or select several and press Hide.
Visitors no longer see it, and it's left out of every download. On the Photos tab it's dimmed and marked Hidden.
Show in the gallery, or Show in the bar, brings it back.