Start by downloading and installing the greenfoot IDE via the Download tab above.
go to the scenario option and make a new java or stride scenario
So i downloaded greenfoot and it said that I needed a JDK for it to run so I downloaded the latest one and it still is saying it won't work without JDK
You need a JRE with the JDK included. Is that what you downloaded?
Optionally, you can download the USB version of greenfoot which have them included in it.