In Grand Theft Auto Online you can do quite a few things as soon as you step into the game. However, if you want access to some of the cooler activities, you'll need to raise your rep. The best way to level up is by completing jobs. You can do this alone or with other players, and there are advantages and disadvantages to both approaches.
The default approach is to take on jobs and missions with your crew or random other players. The advantage here is that the stakes are higher. You'll earn more money and more reputation points with each successful job. You also don't have to be the best to win. You can rely on your teammates to help you earn the win and score the cash and points. Unfortunately, if you lose, you don't get much of anything, and if you're pitted against a solid team who plays together regularly, you could be in for a long run.