I haven’t read the books and i’ve watched the movies all each once whenever they came out on DVD, meaning sometimes more than a yearly gap in between them. I just watched the end of the series and i had mostly understood it except for one thing, what the hell was wrong with Dumbledores hand? Apparently his hand was turning black and whatever was wrong with him was going to kill him withing a year at most. Now maybe i missed it or forgot but that seemed to come out of nowhere.
There was a curse on the ring he found that was one of Voldemort’s horcrux.
Did they mention that at all at any point other than the couple seconds of the flashback in the last movie?
Yep, he put it on. He was trying to resurrect his sister, who died from a misfire spell…which he is not sure came from his wand or not. Remember, that ring had the resurrection stone as its jewel.
I think it was mostly lost in the book to movie translation. One of many things that got cut.
just to expand on the answer a bit:
as has been said, the ring was cursed. dumbledore knew the ring contained the resurrection stone, and succumbed to the temptation to see his sister once more (and perhaps learn it was not he who killed her). he manages to return to hogwarts and is tended to by snape. snape is able to slow the curse and contain it in the one hand, giving dumbledore perhaps a year to live. this is the moment when dumbledore tells snape to kill him when the right moment presents itself.
and yes, it was pretty much glossed over in the movie.