OpenSCAD User Manual/CSG Modelling

union

Creates a union of all its child nodes. This is the sum of all children.

Usage example:
union() {
        cylinder (h = 4, r=1, center = true, $fn=100);
        rotate ([90,0,0]) cylinder (h = 4, r=0.9, center = true, $fn=100);
}

difference

Subtracts the 2nd (and all further) child nodes from the first one.

Usage example:
difference() {
        cylinder (h = 4, r=1, center = true, $fn=100);
        rotate ([90,0,0]) cylinder (h = 4, r=0.9, center = true, $fn=100);
}

intersection

Creates the intersection of all child nodes. This keeps the overlapping portion

Usage example:
intersection() {
        cylinder (h = 4, r=1, center = true, $fn=100);
        rotate ([90,0,0]) cylinder (h = 4, r=0.9, center = true, $fn=100);
}

render

Always calculate the CSG model for this tree (even in OpenCSG preview mode). The convexity parameter specifies the maximum number of front sides (back sides) a ray intersecting the object might penetrate. This parameter is only needed for correctly displaying the object in OpenCSG preview mode and has no effect on the polyhedron rendering.

Usage example:
render(convexity = 1) { ... }