You do not invest in individual stocks until you have a total portfolio of $1 million, and many smart people are now advising $2 million. Until you get there, you spread your money around by investing in quality no-load mutual funds or exchange-traded funds. You want to own some the big name newsmakers - like the 'FAANG' stocks? Facebook, Apple, Amazon, Netflix, Google? Well, almost all of the good large-cap growth funds own them. And many, many other good companies. Funds are professionally managed by people who are experienced in going over all a company's financial data from the past and analyzing current performance and predicting future performance based on what is happening in the real world. Who do you think knows more about that, then or you? When you buy individual stocks, you are acting like you know more than the professionals.
You need some kind of a broker, you need someone to make the trades for you, unless you decide to sign up with a single mutual fund company such as Fidelity or Vanguard. They can help you get started and it won't cost you much money, and what money it does cost you is charged as a very small percentage of the money you have invested. In the meantime, while you contribute money on a regular basis, you start reading books on how to invest in mutual funds and you raed more books and articles on how to do some of your own analysis. If and when you think you are ready to start managing your own money, you can move to a discount broker that will hold a custodial account for you, and charge you low commissions for the trades you make your own decisions about.
So for now, call Fidelity or vanguard or look up some of the other companies that sell funds without 'loads' or upfront commissions and ask how to get started. Some companies will let you start with as little as $50 with minimum monthly contributions of $50 per month.
I would advise opening two accounts, one as a traditional or Roth IRA (for you, I would go with a Roth) and a cash account. The IRA is your retirement account and that is the money you will live off of when you retire. You touch that money for no reason. The cash account will be money that you can tap into if you must. Use it toward a car, your first house, big things, not for everyday needs and those wants that are just that, things you want but don't need. An awful lot of money gets blown on things we want but don't need. The earlier you believe this, the better. Knowing it is nothing, a lot of people know you're supposed to save and delay that self-gratification, but most people don't do it because they don't believe it.
You are 18. I was 25 before I first heard this advice from the first mutual fund broker I met, and I believed it and bought into it, and it changed my life. You have a 7 year head start on me.
It is the rule called 'Pay yourself first'. Have a realistic goal for saving and develop a plan and then a budget based on it. Don't be so optimistic that you put away so much that you can't live, because you will find yourself taking your savings to pay for the things you must have, like rent and food and heat etc. You will get discouraged and might give up on the idea of saving. Start small and while you teach yourself some discipline in how to spend - if you must have that daily coffee, spend $1 at McDonalds and not $5+ at Starbucks, walk four or five blocks or a mile or so instead of taking a ride-share for $3, $5+. Make and bring food from home instead of buying meals for work. Learn to be a tightwad on spending on yourself and you can afford to be generous with others when it can do the most good.
This woman, when I was 25, also taught me this: If you invest $100 every month starting at age 21 (you have a 3-year jump on that) and stop when you are 35, you will have more money at age 65 than if you wait until you are 35 to get started and never stop saving that $100 a month.
This is the rule of compounding interest on your money. Those dollars you put away at 21 will be working for you for 44 years, earning more and more every years as the interest compounds. Of course, the whole idea behind this is that you DON'T stop when you get to age 35 - you stick with it, and you bump up your savings so that maybe by 35, you're putting away $200 or $300 or more every month.
Learn these rules early, believe in them, don't get distracted by the things you would like to have and by what you see your peers doing, and put these rules into practice, and start reading.