You need a brokerage account but they are free.
You need a computer. But that computer doesn’t need to be very sophisticated. I often trade on computers that are years old. The computer I am typing this on is almost four years old and it is my main computer.
In fact, you can trade on your phone or tablet so you don’t even need a computer anymore!
You need an internet connection. I like a fast connection but you don’t really need one. You need a stable connection that doesn’t cut you off all the time. I’ve traded in third world countries where the internet went in and out. I could run my trading operations but it was frustrating.
You need a charting program. There are many great charting programs that are free. I use ProRealTime.com and Stockcharts.com. They both have great services that are free. Real time prices cost money on both of them but position traders don’t need that.
In addition, your broker is almost certainly going to give you free charting. It’s usually OK but I prefer the two above because I can program them with my super tricky indicators.
So the bottom line is that you need to pay for internet and that’s it!
That’s about it!