Per the instructions, you would start at 6.57L of water. Once mashed in, remove grain, and bring water volume to "Boil Size." The instruction imply that after that 60min boil, you will have 13.37L of wort remaining. From that 13.37L of wort you will end up with 10.49L of beer that you can bottle. The rest is trub, yeast cake, and other non-bottle-ables.
Note - until you know your system you will not know for certain what your boil off rate is. Therefore, if I were you I would use 6.57L of water, add enough water to bring it to 10L, boil for the 60min with hop additions, chill the wort, add to your fermenter, and top off until you get back to 10L of water. Alternatively you can extend your boil to get the volume of water you will need; however, if you do that you then have the issue that your boil time for your hops will not be accurate.