If you're ready to start buying individual stocks, download a mobile trading app. You'll be asked for some personal information (like your social security #) which is required by law.
Then you need to connect the app to a bank account in order to transfer money to trade with. This can be as little or as much as you like. If you have a specific stock in mind, check the price and determine how many shares you want to buy. Then transfer that amount. You can always add more later.