What s the difference between gta online and story mode?

The verified evidence describes Grand Theft Auto: San Andreas as a 2004 action-adventure game set in 1992 within the fictional San Andreas state. The game follows Carl 'CJ' Johnson's return home after his mother's murder, his efforts to rebuild his old gang, and his confrontations with corrupt authorities and rival criminals. The evidence does not mention GTA Online or compare it to story mode, so I cannot provide information about the differences between these modes based on the given source.