Can anyone explain Photostream to me?

[PhotoExplosion]

I'm not sure how this works. At the moment the last 1000 photos or so upload to photo stream. Practical for between devices, but I've had an email saying this is going to stop next month.

At the moment, I have my "Photos" program on my computer hard drive which has all my photos in it. (over 50,000)

I have several shared Albums which are shared either just with me, with DH, or with extended family. Will these also go when photo stream goes? These are my year "highlights" if you like, and info sheets from school etc.

Photostream is effectively a back up of the photos on my phone, so am I right in thinking that once Photostream goes the only copy of my photos will be on my phone until I download them to my hard drive? So if I lose my phone, I'll lose all my photos?

I am also confused.
I googled and thought I had figured out that it doesn’t matter because I had something switched on, but I was looking for an album earlier to show DS an old photo and the whole album has vanished. I don’t have that photo, or the others that were with it, anywhere else. It was an iCloud album, I was always puzzled how they ended up there because I had no clue how I did it, but now they are gone.
I though cloud was staying because it just kept saying photo stream, but seemingly they meant iCloud.

https://uk.news.yahoo.com/apple-photo-stream-shut-down-124952355.html?guccounter=1&guce_referrer=aHR0cHM6Ly93d3cuZ29vZ2xlLmNvLnVrLw&guce_referrer_sig=AQAAAEznBxrRpA1ByG85rcqcBzgs3ld28T8PgQ4CT7KQvJGlA4choiVsNnfZ6rgyViSJiUbaKRHtGXBNKaMXQW7fCen3TBkImbwD0muAbbqyPBv2WnES5N4tWvqWCI34fQIKUEaQU1tzfp3NNN4PlqNi5pu_EU49zcxw2qzdbHafBMaL#:~:text=Because%20existing%20photos%20are%20deleted,shut%20down%2C”%20Apple%20said.

I'm glad it's not just me! MIL had a photo album go missing from iCloud, we assumed she'd accidentally deleted it when she changed phones, but maybe not.