Original files are untouched by any edits. No worries on what was done before or if an accidental save occurs. All work is separate from the originals.
A very well considered UI makes edits fast and fluid. You can redo or undo any step without disturbing any other part of your edit. The UI doesn't get in the way.
Most modules, by default, affect the whole image, but have the option to only be applied to masked-off areas (be those drawn masks, parametric ones, or a combination of the two).
On the camera set it to use USB Remote. Open Darktable, on the left side under Import, click scan for devices. The camera should appear. Click on tethered shoot. Next on the right side look for the gear icon above the battery n/a and click it. go to the session options tab, and change the base directory to the location you want to save photos. close that settings window and try taking a picture. It should come right up.
EDIT: There is now an official build for Windows
Whilst official builds exist for Linux and OSX, this isn't the case for Windows (though unofficial versions do exist).