How do Hold and Win slots work, and what tips help players?

I constantly see slots in the lobby labeled Hold and Win, but I still don't completely understand the mechanics. I read that symbols somehow lock in place on the screen while the rest spin again, but I don't get when it triggers and what the player is supposed to do. Can you actually influence this, or does it all come down to pure chance? I'd love to hear from experienced players about how they approach these slots and if there are any tips that genuinely help.