People like to pretend stocks are some kind of scheme by the big bad CAPITALIST MACHINE to oppress the workers and enrich the wealthy but that's not what the stock market is about. It's what happens when people who have no idea what they're doing throw their money into financial products and lose everything, but whether you know it or not, your money is probably tied to the stock market at some level. The profit you make at the stock market is directly tied to the amount of money you're risking, and the amount of risk you're willing to accept. No risk means no reward, lots of risk means you can be billions in the hole.
Stocks are essentially lending money in exchange for a tiny bit of a company. If the company does well, you get paid back an amount depending on how much of the company you own. You can sell that bit of the company and then someone else will get paid instead, but you get to keep the money off your sale. You usually also get to have a say in how the company works if you own enough stocks, as you own part of the company now.
Selling stock allows a company to expand more than if it had to slowly save up its profits. You can only mortgage your assets once, but as long as you can convince people to lend you money, you can make money with stocks. The more a stock is worth (=the more trust existing or prospecting lenders have in you), the more likely people will be willing to buy parts of your company.
By not selling every part, or keeping a small set of parts for employees, the company can also directly profit off of price increases.
There are also companies like co-ops where the workers all own part of the company. That means they get a say in how the company is run, as the workers collectively have more power than even the CEO, for better or for worse; convince the majority of a terrible business plan and the entire coop goes to hell, even if the CEO warns everyone about how bad an idea something is. On the other hand, when someone tries to cut costs by doing mass firings, the workers can come together and put a stop to that. This also motivates workers, as the stock they get paid is worth more when the company is doing well. This doesn't have much to do with the stock market, as these stocks usually aren't traded publicly, but it's just an example of stocks being used to improve the position of the working class. Unfortunately, co-ops like these can't use stocks to attract investment, so these companies don't grow as much, and you don't see too many of them as a result.
You can do a lot of things with stock if you enter the stock market. Most of that is actually contracts about how you're going to treat a stock you own or want. For instance, you can borrow a stock from someone else for a modest fee, sell the stock off, wait a bit for the price to drop, then buy it back, pocketing the difference. If you misjudge the price difference, you end up paying more than you've sold the stock for.
You can also do the inverse, basically buying someone's promise to sell you a stock for a certain amount of money in a certain amount of time, hope the stock is actually worth more than what you've paid by the time the exchange happens, and get expensive stock for cheap. Once again, this can lead to a situation where you make a loss, for instance when the stock drops in price and you've paid more than if you would've bought the stock directly.
It's basically all betting and betting on other people bettings. Making money through normal stocks takes a long time, as the company you've bought stocks of may take years to reach the growth you've funded, and these bets can make you a lot more money in a shorter amount of time. However, you're not obligated to do anything crazy with your stocks; you can just buy them, hold on to them, and make a small profit over the money the company pays back.
Companies that don't sell stock and still compete with stock based companies often have other investor deals. Without these kinds of loans from people with free capital, it can take decades to collect enough money to pull off growth that would take a year with stocks or other loans. If you're starting a business, they can help you achieve your goals and bring your products and services to everyone for affordable prices. If you've got more money than you need, you can use stocks to help someone else get their business running, and you get a bit of cash in return. If you think you've got a good idea for how to run the business, you can buy a significant chunk of stock and weigh in on how that business can work best.
Stock also has another upside: the stock market allows you to take money you have pooled (be it retirement funds or just some money you've got floating in your bank account) and invest it in some safe bets which make about 2 or 3 percent profit over a long time. If you don't do that, the amount of money you've saved will remain the same, but because of inflation, that money will be worth less over time. A million dollars was enough to retire on a few decades ago, but if you've saved a million and stopped back in the day, you won't have enough to retire now because everything has gotten more expensive. That's why pension funds usually invest part of their money into stock markets. Minor fluctuations over time (like a company losing a quarter of its value this year and making everything back next year) aren't very important if you're saving money for 30 years in the future.
There is a massive downside to stocks, though: they're a quick way to lose money, and way too many people get sucked into complex financial contracts they have no understanding of. Take the Robinhood traders that didn't realise they were signing contracts that could make them owe tens or hundreds times the amount of money they put in. You could also make a mistake and loan a lot of money to a company in exchange for stocks and end up with nothing when the company goes bankrupt. You could also sell too early and lose all of your profits to the minor fees stock brokers demand to do the actual stock trading for you, as everything needs to be registered properly.
Another problem with the stock market is that large funds, such as hedge funds and pension funds, need people to run them. There's an incentive for those funds to make as much of a return as possible, regardless of what happens to the companies they buy parts of. When these funds come into control of a company, making decisions that only make a profit in the short term and screw over everyone in the long term can make those funds a lot of money, at the cost of the businesses they buy. Businesses can protect themselves from this (by not selling more than 49% of their stock, for instance, or by having 51% or stocks in the hands of their CEO/leadership, so any decision can be overruled). However, companies often like the idea of making money more, plus the more control they give to stock holders, the more their stock will be worth.
This stuff is also why there are rules about all of this. Look at the lives ruined by cryptocurrencies to see what happens when you don't have them. In the end it's just people making mistakes and ruining their own lives, but as a society we're better off protecting each other from making those mistakes.
When it comes to anticipating rise in/fall of value, you don't need stocks. There was a massive prospective market on pogs and beanie babies. People still buy action figures, Pokémon cards, and action figures to hopefully make a profit one day.