The netinst liveUSB does not include any GUI. As far as I know, you have two options: (1) install the current core system, and install a graphical user manager afterwards, or (2) install another version of debian which contains a GUI on the USB.
(1) - Install the core system and install a graphical environment - this could be: Gnome, KDE, Xfce or ay other. See more at https://wiki.debian.org/DesktopEnvironment
Those graphical environment have different focus areas, for example: xfce is lightweight, and you would install xfce on a machine that have low ram. KDE is fancy, you would install KDE if you need eyecandy. Gnome is just Gnome, simple and just straightforward - with an mix of everything.
(2) - Reinstall the usb with a debian.iso that contains a graphical environment.
Edit: There is nothing wrong with your question. I would ignore Vinz, some people have pleasure of hating.
Edit 2: To Vinz, go write a comment to these questions, and tell them that they are too Debian specific - now where you are at it:
Debian stucks at formatting 33%
How can I install only the basics in Debian?
Debian "Graphical expert install" mode
Sorry Tom for me making the edits, it's because I can't comment yet.