Connect

shortcut ALT + 1 in edit curve mode

Connect is not actually a CURVEmachine tool, it's just Blender's native Make Segment tool, but keymapped by CM and exposed as Connect in the menu.

It's purpose is to create a segment from a point selection, and it can be used to connect the end points of two splines.

If you connect the two end points of a single spline, then it will be made cyclic. Toggling spline cyclicity as the same effect.

Selection

2 Points