Hi Pierre, are you having problems with any one particular part?

Basically there are 2 motions that you have to do - first the click and drag to make the construction line, and then a press and hold on the little launcher tag. After that it should be pretty self-explanatory, just fill in the menu item and snap to the points...

Once you get used to it, you should be able to activate it pretty quickly.

Please let me know if you continue to have problems with it.

- Michael