Ride along a curve carrying three perpendicular arrows. Curvature is the circle that fits best.
On the helix, curvature and torsion never change. That is the whole reason a helix looks the same from every point along it.
Drag to orbit, scroll to zoom, slide to travel.
A curve in space has no preferred directions of its own — but at every point it can build three, out of nothing but its own shape. Together they are the moving frame, and they travel with you like a cockpit.
T points where you're heading. N points the way you're turning, perpendicular to T, toward the inside of the bend. B is perpendicular to both — it names the plane you are momentarily turning in.
The circle is the honest measure of how sharply you're turning. Of all circles through your position, exactly one matches the curve's direction and its rate of turning; its radius is 1/κ. A gentle bend gets a huge circle, a tight one gets a small circle, and on a straight stretch the circle escapes to infinity and κ drops to zero.
Torsion is the other half of the story: how fast the curve twists out of that circle's plane. A flat curve has τ = 0 everywhere, however wildly it bends — try the ellipse. A helix has both constant and nonzero, which is exactly what makes it a helix, and together κ and τ determine a curve in space completely up to where you put it and how you turn it.