>>10591131It's essentially just that index funds invest in almost everything so if the value on average of the entire economy goes up then so does the value of your investment and if everything goes down, your investment follows suit.
The thing is that aside from major recessions things never go down across the board and after recessions indexes always recover, albeit slowly, so you'll end up back where you were.
For those reasons it's a better way to save money than a bank but it's very low risk so it's not really a great way to generate passive income either.
Keeping money in the bank can end up costing money though. Most people assume if they save money in a savings account then it just maintains at a set level but that's not how the value of currency works.
It's worth learning a little bit about at least. The earlier you acquire that knowledge and start putting it into practice, the better off you'll be later on.