This feature is used when a player wishes to use a joystick/game-pad with the game.
In order to use the joystick properly with EDuke32, you must check the joystick check-box under the configuration tab of the Eduke32 pre-game setup.
After that, you run the game.
To set up the joystick, go to the Options menu then click on Joystick Setup (Note: if this menu is blue, your joystick/game-pad is either not plugged in properly, or you do not have the correct drivers installed.)
Under joystick setup there are several menus available.
Setup Buttons allows you to assign the various controls to the buttons on your joystick/game-pad. Edit Axes allows you to assign basic movement parameters and/or digital controls to your joystick's X and Y axes, and Rudder and Throttle axes (on most game pads, X and Y is the left analog joystick and Rudder is the right analog joystick's X axis and Throttle is the Y axis.) The basic movement types are Strafing, Looking Up and Down, Movement and Turning. There are also controls to control the sensitivity of the axis. (Note: with my personal experience with a game-pad, the strafing function has acted ridiculously sensitive and may be hard to control, so it may be wise to set the sensitivity on the axis that uses the strafing control to something around 0.13.) Digital controls make the axis function like a button when the pressed in the designated direction. Edit Dead-Zones allows you to set up to which angle the axis will be maxed out and cut-off. There are controls for all four axes possible.
Overall, playing Eduke32 with a game-pad or joystick will change the experience of the game, and it's always nice to try something new! :)