I am trying to download a map for terraria from my Xbox One to my PC and I'm having trouble figuring it out. How do I transfer my stuff from Xbox to PC?
Save files between platforms are not compatible. Generally, console and PC versions of Terraria are very different, and the console versions are often behind as well.
There used to be ways to do it between Xbox 360 and PC, which involved copying files and converting them with a tool someone made. This doesn't exist or work for Xbox One, though. Depending on what is required, you would probably be violating the Microsoft TOS concerning your Xbox One.
Also, while strictly not a duplicate (because it's the other way around), a similar question and answer are found here.