You can put money ( up to $6k a yr) into your own IRA, and pick investments.

If you have an employer that participates (sponsors) a retirement account ( often matching up to a certai npercentage that you deposit every paycheck) is a 401k

I used to recommend Robinhood just because it was free and no per trade costs or anything, but I think that's pretty common across the board over the last few years.

Either way, the platform doesn't matter a ton (as long as it's free).

Once you're in, you just put money into SPY or something like it. It's basically a single stock that represents 500 of the top companies.

Another bonus for Robinhood, it allows fractional shares to be purchased. So if a single share is let's just say 1000 dollars, a lot of people would have to save up for quite a while just to purchase 1 share. Robinhood (and I'm sure some others) allow you to invest with just those 5 dollars. I pretty much exclusively buy and sell in dollars these days rather than in shares.

I mentioned SPY as the one to buy, but there's probably a dozen or so other S&P 500 indexes by other names, their overall long term value is going to be pretty similar.

I set up recurring automatic withdrawals from my bank account a few days after pay day (into Robinhood) as well as an automatic recurring purchase of more shares every 2 weeks as well.

It's really a set it and forget it thing, you're not trying to buy low sell high or anything - you're just putting in money hoping that the us economy continues to grow. The companies in the sp500 change over time as new top performers rise and others fall, do they're doing the work for you.

Warren Buffett constantly tells people that this is the best long term strategy. Over a short period, a single stock can perform better, but long term trying to buy and sell and play the market just isn't anywhere near as reliable or safe

If sp500 stops growing long term, it's only because America stopped growing