Sonar witch arduino and lcd Grapich (fishfinder)

Hello to all .
my name is Alessandro and I just started to use the Arduino (I apologize for any trivial errors :smiley-confuse :confused: ).
as regards the hardware part I have no problems but what complicates the situation is the software.
I just tried to use Arduino as sonar with the card:

I also took the sketch from this video with graphic LCD display was right for me

With this "Purpose" I have to do a fish finder so that the masses were visible on the seabed as the tips on the display

But once I tried to load the program gave me this error
"Adafruit GFX.h"

I hope you can help me because they are the first trials with Arduino and hope abbiade of scketh more clear to the graph on the display.

Thank you, bye :slight_smile: