I would try to answer in best possible way possible .
Original game :- when you buy a game from a store or download via digital copy from a trusted vendor , and you get a unique key that solely belongs to you . That key is the proof that you have purchased a 100% authentic game and you are not in any way pirating it [ downloading from internet for free ] .
Advantage :- You can get the game as soon as it releases
you can play online - multiplayer
you get support from game forums
you help the companies that make the game .
Cracked games :- When you download a game . free of cost ! from a un trusted source or website or torrents , . when you download the game you will also get a crack or exe file that will over ride the authentication check , and you will be able to play the game offline . however , you won't be able to play online unless there's a multiplayer crack for that game . moreover , It's illegal also .