In the tutorial they made use of guides and alot of layers to organize things.
1. You are going to need to mark your diecuts with a format that the printer is familar with. (This is in the tutorial)
[Magneta for the the diecuts ]
Hex triplet #FF00FF
RGBB (r, g, b) (255, 0, 255)
HSV (h, s, v) (300°, 100%, 100%)
[Cyan for the fold
Hex triplet #00B7EB
RGBB (r, g, b) (0, 180, 247)
HSV (h, s, v) (180, 100%, 97%)
When you layout your document you will choose either inches or cm whichever you prefer and then will need to enable your grid and snap options to snap to grid make sure that things line up.
As a starter I would open the flatsheet.ai file (you will need the development version of inkscape which can open .ai files I am not sure of your system, but the development version can be found
here) an turn on the grid and then set your settings to inches or cm whichever you prefer and then ungroup the object in the flatsheet ai. This way you will get a feel for how things are being layed out. Essentially on your own you want to reproduce the tutorial layout.
Hope this helps