How to make curved shapes in 'edit mode'

in order to make "curved shapes", you should hopefully know a bit of geometry.

A circle is (sometimes) considered to be a regular polygon with an infinite number of sides. A regular polygon is a polygon with all sides having the same length and angle.

A quick exercise: think of a regular triangle, then a square, and just add a side to the shape each time. It will start looking more and more like a circle.

This is a dodecagon, a polygon with 12 sides: [1] it looks a lot like a circle.

By using either the Q button or the scroll wheel in Sandbox, we can make octagons.

Watch this Youtube video from Cube 2 to understand: [2]

to make a circle, you can do any of those options, then use copy, paste and rotate to create the circle.