I have some experience with this.
The latest version of the Nexstar + handset has a serial to USB converter built in. The handset connects to the mount via the telephone-style cable, and you connect your PC to the Nexstar + handset with a mini USB cable.
IMHO, the free Celestron handset emulator software that runs on the PC is dreadful. I have also been unimpressed by other software that is capable of controlling the scope (pointing model, goto) such as Skysafari.
I prefer being at the scope, eyepiece in, and aligning and finding objects with the handset. I then swap out the star diagonal plus eyepiece with the camera when all is good.
So you can do operation via PC, but the Nexstar mount is not up to remote control like the very much more expensive mounts such as the Paramount series.