@dreamin_disney
First, I don't work for any of these companies mentioned but I do admit I'm a big fan of Vanguard and have been investing with them for almost 30 years.
A mutual fund is a collection of many stocks combined. So rather than buying individual stock in let's say Disney, Coca-Cola, Amoco & Microsoft, you find a mutual fund that invests in those companies along with several other companies. It's a safer way to invest because you're not "putting all your eggs in one basket." Index funds are a type of mutual fund that has a goal of keeping returns in line with a chosen stock index such as S&P, et al. Doing this makes it easier to manage which keeps costs down. Vanguard is well known for keeping costs down which means more $$ for the value of the fund.
Mutual funds - Investing in a mutual fund | Vanguard
An index fund will usually say index right in its name, at least those from Vanguard do. Part of what investors look at/compare in a mutual fund besides returns is the cost which is listed with the rest the stats on each fund. So while index funds have lower cost, they tend to have slightly lower returns than non-index funds. I have some of both and my non-index funds shock me sometimes how well they perform. Maybe that's just me and the funds we have. Maybe that is a real difference between index and non index. I don't know and maybe someone with more knowledge can chime in.
Overall, higher risk mutual funds tend to be more volatile, which means they tend to swing higher and lower than others. Highs are wonderfully high,

but then the lows are pathetically low.

Your personal risk tolerance is a factor but for retirement funds, your age is a big factor. When you're 59, you don't have 45 years of future working to make up for a big loss. Our ds20 has
plenty of time until retirement so he can take on more risk by choosing high-earning, more volatile funds. Time and compounding % is what will grow his retirement fund to become sooo much more than what he actually contributes. Compounding means your earnings start producing their own earnings and it just keeps growing. Some mutual funds automatically adjust the risk as the investor ages so that as retirement nears, it's not investing in riskier stocks. Vanguard calls these Target Retirement 20xx with a variety of retirement years to choose from. This takes some guesswork out of it.
A word about big loss. When you hear the news and people crying about their investments dropping so low, such as last March when covid hit, you really only suffer that loss if you withdraw from that fund. That would be like "selling low."
If you leave it there, the market recovers eventually and the value goes back to what it was, or hopefully better. If it's a short dip and recovers quickly that's not so bad. If it lasts a long time, like years, we lose the earning potential that fund would have had.
The worse thing you can do when there's a crash is to pull your money out. Let it ride the waves. This, of course, is a problem for retired folks who HAVE to make withdrawals as their income. The only way around that is for retirees to create a cash buffer of 1-2 year's worth of future income before they retire so that if the market dips, one can choose to not make any disbursements from the retirement fund.
Time is the one thing that benefits
everyone investing, whether you invest a lot or a little bit, so the sooner you start, the better!
9 Charts Showing Why You Should Invest Today | Investing 101 | US News
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