If you're looking to set up a buy & hold portfolio (as opposed to day trading/stock picking/speculation), I like
M1 Finance. No fees, and easy to use. The 'no fees' part is important - that can really sap your earnings over time.
As for portfolio composition, IMO the best place to start is with the All Weather Portfolio. Basically it was a proposal from personal finance book author Tony Robbins and Ray Dalio, co-founder of the world's largest hedge fund firm. (Forbes has him in the top 100 richest people in the world.)
The portfolio assets are divided up like this: 40% long-term bonds, 30% stocks, 15% intermediate-term bonds, 7.5% gold, 7.5% commodities.
Why do I like that portfolio? Well, here's some footage of that portfolio rolling through the Great Recession and covid shutdown periods:
Notice what you don't see there? No huge drops during periods when the stock market took a dive and recessions hit. Imagine it's 2008, shit has hit the fan all over the economy, and you just lost your job. And you take a look at your portfolio to see how bad the damage is, and it's... next to nothing? Hallelujah!
There's definitely portfolios out there that will earn you more money
in the long term, but don't underestimate the value of not shitting your pants when things take a downturn!
Anyway, I've got plenty more I can say, but that's all I have time to write for now...