The good news is that you'll accrue a pretty impressive amount of cash just by playing though (and completing) the game's main story, and generally playing it smart. Just like the real world markets though, you'll struggle to make money out of these systems until you have a fair bit of money to throw at them. If you want to make some serious money in GTA 5, one of the best things you can do is master the game's stock markets.
Watch on YouTube How to make GTA 5 money fast using the Stock Market and Lester Assassination Missions
GTA 5 Money works the same as it always has on the surface, but the GTA 5 stock market, coming in the form of the very maturely named BAWSAQ and LCN markets, have added a big shakeup to the best GTA 5 money making methods in-game.