You can say : Mafhamt walou Or Maqdart nafham 7ata haja

Oh I see now :) luckily you have an answer from Sana :)

I didn't explained me well, I wanted this phrase :"I can not understand anything", in darija but I have it already, thanks!

Yasmin, what are you asking about? there's nothing in your question, maybe you forgot to attach a link or something?