> Everyone is saying Passive Investing is the best for the average investor, but they never tell you what index fund to buy and more importantly when exactly.

https://www.bogleheads.org/wiki/Getting_started

EDIT: Bogle's main problem with ETFs is that they allow people to get in and out of the market during the day, lending more towards speculation/day trading than long-term investing. With mutual funds, you can only buy at the end-of-day prices instead of the many prices available during the day.

TLDR Less trading is better. You dollar cost average into broad low expense ratio funds, and you will (very likely) end up wealthier in the future.