The iTwin device consists of two modules with USB connectors at one end and a proprietary connector at the other; they come out of the box conjoined via the second connector. You plug the plug iTwin into the PC whose data you want to share, and it appears as a virtual CD-ROM drive from which you install iTwin's client software.
Once the software is set up, an iTwin icon appears in Explorer's "Computer" object. Drag into it any files you want to share out across iTwin. This doesn't change the location of the files themselves; they're shared out from wherever they happen to be. Next step: detach one end of the device and take it with you. Plug it into your notebook (or any other PC that has a USB port and allows software and devices to be installed), set up iTwin there as well, and you'll see on that computer a folder with all the files shared out on the first one. File sharing works in both directions. From either computer you can open files, add files to your home machine from your remote one (files added in this fashion show up on your desktop), and make local copies of files from your home machine.