2-Point Sketch Planes

Tap and hold on a curve or on the grid (in an orthographic view if on the grid) until you see a red dot and dashed lines.
Tap and hold again on a curve or other point on the grid until you once again have a red dot and dashed lines.
Orbit the camera - the plane between the points is called a 2 point sketch plane. This enables you to sketch curves at angles.
You can use 2 point sketch planes between two curves to easily connect two curves.
When you are done with the sketch planes, double tap on empty space or tap the checkmark at the bottom of the interface to exit.