Hi,
To configure my Time Machine I did this :
Go to the Web interface and create a share folder Timemachine i.e. (in the options, unselect Windows, Apple, Draft, share... anything)
Go to Time-Machine label, and activate it.
Select the folder you created.
Push valid button.
Then, choose a a Target host name (simple like "marcivana")
Enter the Mac adress of the ethernet connexion of your Mac
Click to create the image (wait for 5 minutes or more if you want to be sure it's well done)
The in your Mac, go to Time machine, and select the Time Machine drive... Enjoy!
If you have any problem contact me in PM, I'm French too, perhaps it will be easier.