I have taken a look at your file, the reason that you could not close
the vectors, is that there are some duplicate lines and lots of near duplicate lines.
I am guessing that these also exist in the original Moi design.
The first step to cleaning these up is to use the "Select all duplicate vectors" tool from Main Menu Bar > Edit.
Once you have selected the duplicates, press delete on your keyboard.
However, this is only a part of the clean-up required for the file that you sent me.
There are a lot of "nearly" duplicate lines that also need to be deleted.
You just need to select these one by one and delete them.
Once you have deleted the unwanted vectors, you can choose to join the remaining vectors.
As regards node editing, it is covered in the help file
(The link should hopefully work if you copy and paste it to your browser, I have assumed that you have a french language copy of Windows)
But idealy, with Cut2D, your designs should be fully designed in your CAD package, before importing in the design.
I have emailed your file to you with the deletions.
I hope that this helps.