Here is a random bit of code I found in a tutorial:

difference() {
union() {
// teardrop shape
sphere(r = 20);
translate([0, 0, 20 * sin(30)])
cylinder(h = 30, r1 = 20 * cos(30), r2 = 0);

// dollop
translate([0, 0, 30 + 20 * sin(30)])
sphere(r = 6);
}
//cut out slot
rotate([45, 0, 0])
translate([-20, 0, 0])
cube([40, 5, 40]);
}

What is the meaning or function of:

1. the round brackets - Difference () Union ()
2. Wiggly brackets {lines of code}
3. stuff inside square brackets [ ]

I know that // indicates a coder's comment that does not get read when the code is run.

OME