empty gun/magazine
slide back
bolt open
lean shotgun left to about 11 O'clock position (just so the shell doesn't fall out)
drop shell in the ejection port door brass end in back just like how you're supposed to load the gun
push slide forward, closing bolt, ready to shoot again
edit: looks like MikeD and I were posting at the same time and after watching the linked video, my description may be classified more as a tactical reload than a ghost reload.