When reading or talking about casino games, you might hear someone refer to them as skill games or games of chance. For example, blackjack is considered a skill game. Slots are a game of chance.
The difference between skill games and games of chance is there’s more or less a right and wrong way to play games of skill, and if not right or wrong, then definitely optimal and not optimal. You can learn these by studying various books and websites, then practice what you learned at the casino.
But games of chance? These are totally random. There’s not anything you can really do outside of cheating to gain an edge playing those.
That all said, skill games are only skill games if you yourself become skilled at them. Otherwise, they might as well be games of chance.