Difference between bad and good ending?

[M a i s]

Haven't really understood the difference when looking it up.

[Hurkyl]

Are you asking for the mechanics, or the actual details of the endings?

Mechanically, there's one choice where you make the "wrong" one and the chapter plays out in a normal fashion, ultimately concluding with the bad ending. Then it's immediately retconned as a "what if" scenario that Makoto imagines and you're sent back to the choice to try again.

I guess... there's also a third ending: a sort of "golden" ending at the end of school mode. I believe this wasn't part of the original release of the game: it was added in (along with school mode) when Danganronpa 2 was released. It's mainly just a bit of fanservice for people who like the cast and want to see an ending where they never suffered through the events of the main game, and it's a vehicle for the character-specific ending sequences that you can get out of school mode.

(Note that school mode contains a bit of a spoiler for the second game. It won't ruin the game for you, but there is a specific aspect of the Danganronpa 2 experience that will likely be changed a lot for you if you get this spoiler)