To open / close a Bezier curve
A marking menu appears.
The start and end anchor are connected or disconnected depending on its current state.
You can use the options in the option box to further refine the curvature between the start and end anchors for a closed curve.
You can also close a curve from the Bezier Curve Tool.
To close a curve from the Bezier Curve Tool
The two ends are joined and the curve is closed.