You will usually only rotate around one axis, leaving the unused fields on 0, I guess. If you want to rotate around more than one axis, please note: The order of the rotation applies is y-axis, x-axis, and then z-axis. You can think of it as the earth position coordinates: x is the longitude, y is the latitude, and z is the rotation at this point of the earth around your bodies axis. (I wonder if that makes it any clearer ;)

Warning

Rotate is absolute, not relative!

 s3d_rotate(object, 90,  0, 0);
 s3d_rotate(object, 180, 0, 0);
 // object will be rotated 180 degrees around the x-axis, not 270 degress!