All investment funds charge fees, there are different kinds, some charge admin fees, entry fees, pretty much all have a management fee, etc. The fees are not added on top, they come out of the investment.
The number you want to look for is the TER - Total Expense Ratio. This tells you what % of your investment is going to fees. When people talk about low cost tracker funds, something like a Vanguard FTSE tracker, the TER could be as low as 0.07%. If you're buying a specialist, actively managed fund, it could be 2% or more.
I don't invest in oil and gas so I don't know anything about how USO works, but it looks complex. Buying futures in a crisis is definitely very high risk. It's good general advice to stick to investing in instruments/sectors that you have some knowledge of.
Knowing that you don't know is a very good start. Be really careful about youtube videos. There are a lot of people claiming to teach you trade etc. Ask yourself, if they are a successful trader, why the hell are they putting all their efforts into making youtube videos about it? They're not successful traders. They're making money from advertising, commissions, selling overpriced courses, etc etc. Just like the MLM scams, they have to give the impression of success to hook others in.
Anything exciting, flashy, urgent etc is generally bullshit to sell you something. Find a nice boring, slow, academic course and put the time in, learn from first principles. Khan Academy has great free resources.
Re eToro - their business model is not the same as a broker taking a small commission on each trade. They don't make their money off people directly holding any assets. They are primarily a short term trading platform. The large majority (around 80%) of retail accounts lose money trading, and that money goes to eToro. For trading accounts they don't actually even hold the asset, they just set a price range and let you bet on movements. You're essentially betting that you're smarter than their professional traders.
People love thinking of themselves as traders instead of gamblers and the trading platforms are very keen to encourage that. Trading is not investment, it is gambling. With a lot of specialist knowledge, it is possible gain an edge. If you don't know what you're doing, you may as well just give the money away, you'll feel far better about it.
The worst thing that happen is having a run of good luck and thinking you're good at it, that's how people end up losing everything chasing their losses. People tend to think that if they made money, that was a good decision, without taking into account how much risk they took.
Platforms like eToro pay very, very high commissions to affiliates - $500 CPAs. It should tell you something that gambling affiliates and trading affiliates go to the same conferences. I was a gambling affiliate for years. For all its faults, at least the gambling industry is not trying to mislead people that they're making rational financial decisions.
Fool.com is at least 50% bullshit and should never be relied on by anyone for anything. Their business model is pure clickbait. Anyone can write anything for them if it gets views. I have worked with writers who have written for them who know literally nothing about investment. They look at what posts get views and try to use the same formula. There's no comeback or downside, no-one is building a reputation there, many aren't even using their real names.
I highly recommend a book called 'Thinking, Fast and Slow' by Daniel Kahneman. It's not about money, it's about recognising basic human psychological biases and overcoming them. It helped me a lot.