Even that I don't really know much about. I'm not even sure HOW to buy index funds, or what to look for etc. I'd have to try to take the time to figure it out, but not like I have much money left over anyway after expenses so I mostly stick with the ESP now days. I have some other stocks I'm sitting on but have not bought in a while.
Most extra money now days I just invest into my property anyway. Next time I cash out some of my ESPP it will probably be for a septic tank install.
If you're a reader, I recommend The Intelligent Investor.
HOW to buy index funds....just buy them in whatever broker you use. On how to pick them...that's a lot of personal how do you want your money invested.
The S&P500 index fund(there's many versions, pick any) is fairly diversified and the recommendation of Warren Buffet. For the index funds, typically a low expense ratio is better. SPY and VOO are 2 I'm in. VOO is lower expense ratio. I use the index funds and then make some smallish gambles on individual stocks.
It all depends on your strategy or outlook on your investments. Some are for the long game which is better suited for the index funds. Others are quick gambles people take.
What some people are doing now is trying to get into a lot of sector ETFs. I've thought about converting my stuff into more of a SP500 then split some out to do some SP500 sector ETFs.