Control points (also called "nodes")
Yellow square control points are corners, and teal circle control points are curves.
You can add a square control point with a left click and a circle control point with a right click on a line or the outline of a shape.
A blue control points indicates the currently active point. You can select a different control point to edit by left clicking on another point.
You can left click and drag a point to transform the shape.
You can transform a square control point into a circle control point by selecting it and pressing the "Space bar" on your keyboard, and vice versa.
You can delete a control point by activating it and pressing the key "Delete".