He shows instructions on how to perform the required modification to get the IF output of the ICOM, and also shows how to interface the PC with the ICOM so that it may be controlled directly via HDSDR.
For people already with expensive ham radios, the RTL-SDR can be used as a cheap panadapter. A panadapter is device that allows you to visually see the RF spectrum and waterfall being received by the ham radio. There are multiple (expensive) commercial panadapters available, but combined with a PC or laptop, the RTL-SDR will work just as well.
In this video YouTube user akdude47 shows a tutorial on setting up the RTL-SDR as a panadapter for a Yaesu FT-857. The setup involves connecting the IF output of the radio to the RTL-SDR, and putting in some settings into HDSDR.
How to setup a RTL SDR with HDSDR and a FT-857 for a panadapter and second receiver.