[GRASSLIST:5664] new, new, new, -tcltk GUI

(i'm new, very new)
i'm trying to access the -tcltk environment but it shows me this message :
grass -tcltk...

starting GRASS...

WARNING : The Wish command (wish) was not found!
please check your GRASS_Wish environment variable.
use the help option for details.
switching to text based interface mode.
_______
what i have to do ?