# translate([0,0,-50]) cylinder(r=5, h=100,$fn=50);

When ever you put a # in front of something it will display that object. So you will see a cylinder translated down to z=-50 and going up to z=+50. That object is being subtracted from the hollow sphere. You might have to do a Design/Render followed by a View/Animate to see the # object.

You can't see inside of the hollow sphere very well, but you could make it so you just get one hole by changing that line to:

# cylinder(r=5, h=100,$fn=50);

Now the cylinder is just as tall but it starts with its bottom at the origin. If you want to see inside the sphere and how the cylinder is positioned, you might try cutting away the first quadrant. Try this code so you can look inside:

sphere_with_holes();


module sphere_with_holes() {
difference() {
sphere(r=20, $fn=40);
sphere(r=18, $fn=40);
#cylinder(r=3.375, h=100, $fn=50);

cube([500,500,500]); // cut away the 1st quadrant
}
}
Well, nicely defined by the code....I will try this code later. Generally, as a standard printer needs directions to let it know what to do ordinarily from some kind of word preparing archive the printing.