Startx is a command line tool used in Unix-based systems, including Linux, to launch the X Window System (X11). It is typically utilized to start a graphical user interface (GUI) environment after booting into a command line interface. By running the startx command, the X display server is initiated, which interacts with the graphics hardware and manages the display, windows, and input devices. It reads the user's configuration file, .xinitrc, which lists the programs to be executed upon starting the X session. By default, startx uses the twm window manager as the default graphical interface. However, users can customize this by modifying the .xinitrc file or specifying a different window manager as a command-line argument. Once started, the X session remains active until explicitly terminated or the user logs out.