warcraft III : how make a mod

[Sylvos]

Hello.
I would like to create a custom mod for Warcraft III.
I know this is possible because I tried several.
like Warcraft III: Heaven Fall
or Warcraft III: Nirvana
Does anyone know where I can find explanations to create this mode. I am French, so it's good if the explanations are easy and with pictures or videos.
Thank you to all those who take the time to answer me.

 

[BloodDrunk]

You should I think be replacing all modelas and textures and whatnot from war3mpq and so,,,