get a 401k or IRA. put the money into the s&p 500, maybe a vanguard large cap or medium cap, and never fucking touch it for 30 years. even when the market crashes, which it will, simply continue contributing.

as an example: in 2008 when everything crashed, I stayed the course and continued to contribute to my 401k. In 2011, after it all recovered, I basically was up 30% because I didn't panic.

When you get around 50 to 55, you should pull out of index funds and go into cash or something conservative.

also, try to max out the 18.5k contribution limit, but even a little amount will go a long way over time.

oh, and if you don't have access to a 401(k), and don't wanna do an IRA, you can always opt for a normal stock market account with something like TD Ameritrade, and use ETFs. ETFs are basically mutual funds, and a good one is IVV: it reflects the s&p 500.