A circle has 360 degrees. You are going to create 360 little bricks for your circle. The "for" loop runs 360 times. The "math.rad(angle )" converts the angle, which is in degrees, into Radians.
Each time the "for" loop runs, it:
Now comes the tricky bit. Here we use CFrame composition, to avoid using trigonometry. We start off with a CFrame at the center of our circle. Then we rotate by the angle we need. Finally, we move the brick out from the center of the circle. Because this is applied after the rotation, the brick moves relative to the new orientation.
Run this, and you should get a nice little circle.
The above example is a rather large circle. Let's say you want a smaller one. You'll have to do two things:
Ellipses are quite similar geometrically to circles. You just need to make one dimension (x or y) longer than the other:
Notice here that the x dimension is 100*math.cos(i), and the y dimension is now only 50*math.sin(i). You can swap these numbers to change whether the ellipse is longer horizontally or vertically. These numbers can also be changed to alter the length and width of your ellipse.