What do they do exactly? About Graphics and etc.

That really differs from game to game.

But most PS2 remasters for PS3 increase the resolution so the game runs at 1280x720 or even 1920x1080 instead of 640x480, and also increase some of the textures in the game.

In general, it's mostly graphics. Some games get overhauled though, but what I do know is I'm sick of every person and their mother thinking a game like Fallout 3 or Skyrim need a 'remastered' edition. Those games aren't THAT old. How about focusing on new games and stop selling off your consoles just to get the newest thing.

(I don't hate updated games, but the amount of svckers who'll shell out 60 dollars for a game they payed 60 dollars before just to play the same game with slightly better graphics is just absurd and a cancer on the gaming industry because it encourages focusing on already released games being resold instead of new products.)