It's pretty straight forward though you need some soldering skills, especially for the little usb c connector. I used this site: Cable Guide in combination with YouTube videos of Cruzctrl.
In short: You need wire, paracord (for sleeving), optionally techflex (for the shine), some heat shrink, usb connectors and any connectors you'd like to put in between (in my case gx16 aviator). Then you sleeve the cable, put techflex on, solder the connectors, apply heat shrink and you're done. Though that's just a really short write up. It's not overly complicated but also not as easy as it sounds.