The demo prompts your for a mode to be used and several details. Just follow the instructions on the screen and make your selections.
Once the program runs you can use the following keys:
This demo is part of svgalib and can be found in the threeDkit/ subdirectory of the original svgalib distribution. However, it is not installed in the system by default, s.t. it is unclear where you can find it if your svgalib was installed by some linux distribution. Even then, when you have the demo on your system, you probably won't have the sources s.t. it is only of limited use for you.
In case of any such problem, simply get an svgalib distribution from the net. You even don't need to install it. Just make in the threeDkit/ subdirectory. As of this writing, svgalib-1.2.12.tar.gz is the latest version and can be retrieved by ftp from sunsite.unc.edu at /pub/Linux/libs/graphics and tsx-11.mit.edu at /pub/linux/sources/libs which will most probably be mirrored by a site close to you.
svgalib(7), vgagl(7), libvga.config(5), triangle(3), striangle(3), wtriangle(3), swtriangle(3), trisetcolorlookup(3), trigetcolorlookup(3), trisetdrawpoint(3), threedkit(7), vgatest(6), threed(6), accel(6), bg_test(6), eventtest(6), forktest(6), fun(6), keytest(6), mousetest(6), scrolltest(6), speedtest(6), spin(6), testaccel(6), testgl(6), testlinear(6), plane(6)
Donations (by check or postal order) will be appreciated and will encourage further development of this software. However this is strictly on a voluntary basis where this software falls under the GNU LIBRARY GENERAL PUBLIC LICENSE.