If I could only ever give you one piece of trading advice, it would be this:
Don't trade, but invest longterm. By longterm, I mean at least 20 years, and preferably 40 years. Yes, I am talking about buying in your early twentys and holding until your retirement. So for all you just starting to earn an income, here is what you simply do.
Every month, invest at least 10% of your income for that month, by buying an ETF (Exchange Traded Fund) called the QQQ, which is like buying a share in the top twenty tech companies, which are listed on the Nasdaq100 exchange.
This ETF is currently trading around $157, and so you invest according to your income. That's it. You are buying every month, whether price is going up or going down.
For parents, open an account for your child as soon as your little darling is born, and do as I have advised above. By the time your child is 18yrs old, you will have their college fees paid for. :)