Spend some time
Morningstar
and
Diehards
Investing Guide
There are lots of worthwhile books, authors worth reading
Graham, Bogle, Swedroe, Ferri, Buffet, Whitman
Some of the above are Indexing fanatics. The biggest controversy about how to invest is Indexing vs Active management. I hedge my bets by doing both while at all times keeping costs down and biasing to value