My son and I are going to take a run learning our 4th Axis setup in Dolphin. In the video below- It helped a great deal as a primer but we're confused on the 6min 14second spot where you just grab an STL file already created? What is that STL for?

As an example- Say we want to mill out a air rifle stock in 4 axis mode. Drawing will be done in Solidworks. Do I then save that as an STL to use? OR pull in as the IGES which you had a Vid on if I recall??

https://www.youtube.com/watch?v=tbkX4BJgdcw

thanks all.
CG