Line
A straight segment between two points. Lines are the sides of almost every profile, and the entities most constraints act on.
Circle
A full circle: bores, bosses, pins, and the guide circles other geometry is laid out on.
Ellipse
An ellipse with its axes aligned to the sketch plane.
Arc
A circular arc between two endpoints. Arcs round the corners of profiles, blend into lines with tangency, and close the ends of slots.
Bezier Curve
A free-form curve shaped by control points — for organic outlines, cams and anything a circular arc cannot follow.
Point
A standalone point. It draws no edge and adds nothing to the profile; it exists to be constrained against — a pivot hole held at the middle of a link, a probe location, the centre of a circular copy.