Welcome. You are doing well. I'll just echo what others (you included) have basically said, because when getting started it's good to hear things a lot of ways to really get it.
JL Collins is great at explaining investing...here's how he basically puts it...
A 401k or a Roth IRA are basically glasses that you can pour beer (your investments) into. Anytime you buy beer and put it into the 401k glass, then you pay no tax on it now, but you pay it when you decided to drink the beer. Anytime you pour beer into the Roth glass, you pay taxes before filling your glass, but there's no tax when you want to drink:)
Once you have your beer mugs, you need to start putting something into them. Vanguard sells many kinds of beers (index funds). You get to pick which kind of beer you want to fill your mugs with. The most popular beer on this site is VTSAX (sometimes called VTI). When you buy this beer, you are buying a tiny piece of every publicly traded company in the United States (3,581 companies last I checked). So, every two weeks, 50% of my paycheck gets sent to vanguard to buy more VTSAX beer. I'm a teacher, so I pour half of my new beer into a Roth403B, and the other half into a 457 (like a 401K).
People here like to buy our beer (investments) from vanguard and store our beer mugs (our tax designations) with vanguard because they are an outrageously good deal. Their investments are all craft beer quality, and yet they charge less than Busch Lite. To contrast, a typical investment firm sells you Bush Lite, but charges craft beer prices.
That's the analogy that has helped me really understand what was going on.
