Good night,

I installed vnc server under my Debian Machine, via apt-get

I configured it (reading a tutorial), and everything seemed to work fine.

I've done the vnc viewer download client for Windows systems, so I was able to log into my Debian machine in a normal pc running windows.

I insert my ip address, I get connected, and I'm asked to prompt my password. I write it and yes, I am able to connect to the machine

But, there's a small problem: I can't see any graphical interface, I mean, I only see a grey screen with a lot of black dots and my mouse becomes a black "X"

And no desktop ... can anyone help me?

You need to edit your ~/.vnc/xstartup file to start up the X environment of your choice. By default, vncserver uses twm, which is an exceedingly bare-bones X environment, so just comment out the line that starts twm, and add the startup command for your favorite GUI.