My Italian is zero!
You must load the JeeLib library in the correct place on your computer. The method recommended here is to use Platformio: PlatformIO: Compile & upload firmware. Blog post 1/3
But I do not understand Platformio and I do not use it. Instead, I use the Arduino IDE. Here are the instructions that we used before:
Installing Libraries W8.1.pdf (279.4 KB)
This is for Microsoft Windows 8.1, but Windows 10 is almost exactly the same.
It is in English.
You do not need RFu_JeeLib, RTClib, GLCD_ST7565 or EtherCard.