Basic Shapes Review

Sphere

sphere(d = 5);
sphere(r = 10);
*centered around the z-axis by default

Cube

cube(size = [x,y,z]);
defaults to one corner being at 0,0,0 of the z-axis (flat on top on the x-axis)
cube(size = [20]);
cube(size = [10, 15, 20]);
cube(size = [20], center=true);

Quick Note:

when centered, cubes are centered on the x, y, and z-axes

Cylinder

cylinder(h = height, r1 = BottomRadius, r2 = TopRadius, center = true/false);

Parameters

h : height of the cylinder or cone
r : radius of cylinder. r1 = r2 = r
r1 : radius, bottom of cone
r2 : radius, top of cone
d : diameter of cylinder. r1 = r2 = d /2
d1 : diameter, bottom of cone. r1 = d1 /2
d2 : diameter, top of cone. r2 = d2 /2
Center:

center=false is the default, z ranges from 0 to h
center=true, z ranges from -h/2 to +h/2

To create a cone shape, make one radius equal to zero: cylinder(h = 40, r1 = 20, r2 = 0);

Quick Note:

In order to increase the resolution of your rounded objects, you can add the parameter $fn
Usually an $fn value equal to 50 will do, and over 100 is not recommended because it slows performance