What are the main differences between gta online and story mode?

According to the verified evidence, Grand Theft Auto: San Andreas is a 2004 action-adventure game set in 1992 within the fictional state of San Andreas. The evidence confirms this is the story mode featuring Carl 'CJ' Johnson's narrative about rebuilding his gang while uncovering truths about his mother's death. The game is played from a third-person perspective with open-world exploration on foot or by vehicle. However, the provided evidence contains no information about GTA Online, its multiplayer features, or any comparative elements between story mode and online mode. Without verified information about GTA Online in the evidence, I cannot describe differences between the two modes.