Before you begin investing, you need an investing account. I have mine through Fidelity. 

Go to the How to Research page and use either the second or third methods. And through these methods, have a few stocks/ ETF's in mind that you are familiar with or at least understand. You have to know what you're investing in. 

Use the methods on the bottom of How to Research page. Make sure that it is NOT at the 52 week high, make sure that the price IS trending up, and check the annual reports to make sure that their sales have grown within a one year period, they are not in debt, and that their net income IS POSITIVE.

Search up the stock in the investing app that you use and click buy on market and select how many shares you want to buy based on how much money you are able to use. NEVER USE ALL YOUR MONEY IN ONE TRADE! You might end up with $0 in the end. There is always a risk.