Device with Internet access
Smart phone, laptop, or even use one from the library. Sign up and register to a broker. You should look at technical support if you are just starting out.
An online broker and trading platform
Pick your stocks and place your trade.
Investment capital or cash
When you have that capital, you deposit it into your brokerage account. Once the money is in that bank, you are able to use it to purchase stock or investments into certain equities and investment classes.
In general, if you are just getting started, those are the three things you need. It sounds easy, but in order to be successful, there is a lot to learn. Once you purchase your shares you can let it sit.