A CNC machine runs on G-Code, so you will need what's called CAM software that will read your CAD file, allow you to select operations to be run on the CNC machine to cut the part, and the CAM program will then create the G-Code that will run on your machine.
I am not aware of any free downloadable CAM software other than demo versions, but there probably is some. MasterCAM is popular but very very expensive. I would look at OneCNC, it has a very loyal user base.
Or you can write the G-Code by hand, it is not hard to learn, and if you are not frequently making new parts, it is probably not worth the investment in CAM software. But if you often do make new parts, it is a HUGE time saver.